Add multiplayer bots, typing languages, and rework the UI layout

Multiplayer
- Quick match: POST /api/multiplayer/quickmatch returns whichever room is
  still filling, or opens one. Players never see a room code; joining by
  code stays for racing specific people.
- Bots fill quick-match rooms after a short wait so a new game is never an
  empty lobby. They only ever join quick-match rooms, never a room opened
  by code. One or two per room, drawn from separate ~40 and ~80 WPM tiers so
  two bots are never near each other's pace, and they stall to correct
  mistakes rather than typing a clean straight line.
- Live player count via GET /api/multiplayer/online, shown on the
  Multiplayer control and under the main menu's Multiplayer button.
- Per-racer colours: you are the theme accent, opponents take distinct hues
  that stay the same from lobby to race.
- The countdown no longer holds the room lock for its full three seconds,
  which is what reset clients mid-countdown.

Typing languages
- 16 languages for the generated-word modes, each with its own
  high-frequency vocabulary rather than a translation of the English list.
- Picker in the top-right rail; non-English uses its own list at every
  difficulty tier instead of falling back to English words.

Fix UTF-8 accuracy in the game core
- update_game_state mixed byte and character counts: total_characters_typed
  accumulated byte-length deltas while total_correct_characters compared a
  char index against that byte count. Equal on ASCII, so it went unnoticed;
  a correctly typed Spanish passage scored 6%. The old byte slicing would
  also have panicked if an index landed inside a multi-byte character.
  Rewritten char-based, with regression tests.

Programming mode
- Replaced prose about programming with real code: 26 syntax-highlighted
  snippets across JavaScript, Python, Rust, C/Go/Java and shell. Single-line
  by necessity, since the typing input is a single-line field.

Layout and readability
- One icon rail arrangement on every screen: Settings/Store under the
  wordmark, Language/Theme/Friends/Account top-right, Stats/Leaderboard/
  Multiplayer bottom-right.
- Main menu: mode picker moved out of the Single Player button, which it was
  notching a divider through and pushing the label off-centre.
- Escape returns to the menu, closing any open popover first, and confirms
  before abandoning a live race.
- Split --text-color and --sub-color per theme; they shared one value that
  measured 3.65:1 against the background, below the 4.5:1 body-text floor.
- Semantic colours used in exactly one place each: gold for a personal best,
  amber for the race countdown and the mobile-result badge.
- Passage now sits in the same place on the typing and end screens, and its
  column is a whole number of characters wide so wrapping cannot leave a
  permanent gap on the right.
- End screen: keystrokes and a correct/wrong/extra/missed split, attribution
  carried over from the typing screen, and a graph with a separate error
  axis, axis titles including seconds, and smoothed lines.

1 files changed, 22 insertions, 0 deletions

diff --git a/data/packs/general.json b/data/packs/general.json
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+++ b/data/packs/general.json
@@ -0,0 +1,22 @@
+[
+  {"category":"general","content":"The quick brown fox jumps over the lazy dog.","attribution":"Traditional pangram"},
+  {"category":"general","content":"Simplicity is the soul of efficiency.","attribution":"Austin Freeman"},
+  {"category":"general","content":"The Pacific Ocean covers more of the planet than all the continents combined. It stretches from the icy waters near Antarctica to the Arctic Circle, and its deepest point, the Mariana Trench, plunges nearly eleven kilometers below the surface.","attribution":"General knowledge"},
+  {"category":"general","content":"Honey never spoils if it is stored properly. Archaeologists have found pots of honey in ancient Egyptian tombs that are thousands of years old and still perfectly edible, preserved by its low moisture content and natural acidity.","attribution":"General knowledge"},
+  {"category":"general","content":"A single bolt of lightning can heat the surrounding air to temperatures hotter than the surface of the sun. The rapid expansion of that superheated air is what produces the crack of thunder we hear moments later.","attribution":"General knowledge"},
+  {"category":"general","content":"Octopuses have three hearts and blue blood. Two of the hearts pump blood to the gills, while the third circulates it to the rest of the body, and the blue color comes from a copper-based protein instead of iron.","attribution":"General knowledge"},
+  {"category":"general","content":"The Great Wall of China was not built all at once. It was constructed and extended over many centuries by different dynasties, each adding new sections and rebuilding older ones to defend against invasions from the north.","attribution":"General knowledge"},
+  {"category":"general","content":"Bamboo is one of the fastest growing plants on Earth. Some species can grow nearly a meter in a single day under the right conditions, which is why it is used so widely in construction and manufacturing across Asia.","attribution":"General knowledge"},
+  {"category":"general","content":"A day on Venus is longer than its year. The planet rotates so slowly on its axis that it takes longer to spin around once than it does to complete an entire orbit around the sun.","attribution":"General knowledge"},
+  {"category":"general","content":"The invention of the printing press in the fifteenth century transformed how knowledge spread across Europe. Books that once took months to copy by hand could suddenly be reproduced by the hundreds, making literacy far more accessible.","attribution":"General knowledge"},
+  {"category":"general","content":"Sharks existed long before trees. Fossil evidence suggests that sharks have been swimming in the oceans for more than four hundred million years, while the earliest trees did not appear until tens of millions of years later.","attribution":"General knowledge"},
+  {"category":"general","content":"Antarctica is technically the largest desert on the planet. Despite being covered in ice, it receives very little precipitation each year, which is the defining characteristic of a desert rather than temperature alone.","attribution":"General knowledge"},
+  {"category":"general","content":"The first computer programmer is widely considered to be Ada Lovelace, who wrote an algorithm for an early mechanical computer in the eighteen forties, decades before any machine capable of running it was ever built.","attribution":"General knowledge"},
+  {"category":"general","content":"The human brain generates enough electricity to power a small light bulb. Billions of neurons firing electrical signals at once produce roughly the same wattage as a dim household lamp.","attribution":"General knowledge"},
+  {"category":"general","content":"The Eiffel Tower grows about six inches taller in the summer, as the iron structure expands slightly in the heat and contracts again once the weather cools.","attribution":"General knowledge"},
+  {"category":"general","content":"A group of flamingos is called a flamboyance. The birds get their pink color from the pigments in the shrimp and algae they eat.","attribution":"General knowledge"},
+  {"category":"general","content":"Venus is the hottest planet in the solar system, even though Mercury sits closer to the sun. A thick blanket of carbon dioxide traps heat at the surface.","attribution":"General knowledge"},
+  {"category":"general","content":"The shortest war in recorded history was fought between Britain and Zanzibar in 1896. It lasted around forty minutes before Zanzibar surrendered.","attribution":"General knowledge"},
+  {"category":"general","content":"Bananas are botanically classified as berries, while strawberries are not. The classification depends on how the fruit develops from the flower, not on taste or size.","attribution":"General knowledge"},
+  {"category":"general","content":"The Amazon rainforest produces roughly twenty percent of the oxygen found in the planet's atmosphere, earning it the nickname the lungs of the Earth.","attribution":"General knowledge"}
+]