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, 17 insertions, 0 deletions

diff --git a/data/packs/philosophy.json b/data/packs/philosophy.json
new file mode 100644
index 0000000..7c9aee7
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+++ b/data/packs/philosophy.json
@@ -0,0 +1,17 @@
+[
+  {"category":"philosophy","content":"Waste no more time arguing about what a good man should be. Be one.","attribution":"Marcus Aurelius, Meditations"},
+  {"category":"philosophy","content":"It's not what happens to you, but how you react to it that matters.","attribution":"Epictetus"},
+  {"category":"philosophy","content":"It is not that we have a short time to live, but that we waste a lot of it.","attribution":"Seneca, On the Shortness of Life"},
+  {"category":"philosophy","content":"The beginning is the most important part of the work.","attribution":"Plato, The Republic"},
+  {"category":"philosophy","content":"All men by nature desire to know.","attribution":"Aristotle, Metaphysics"},
+  {"category":"philosophy","content":"I think, therefore I am.","attribution":"Rene Descartes, Discourse on the Method"},
+  {"category":"philosophy","content":"It does not matter how slowly you go as long as you do not stop.","attribution":"Confucius, Analects"},
+  {"category":"philosophy","content":"A journey of a thousand miles begins with a single step.","attribution":"Lao Tzu, Tao Te Ching"},
+  {"category":"philosophy","content":"The only true wisdom is in knowing you know nothing.","attribution":"Socrates"},
+  {"category":"philosophy","content":"Stoicism is a school of ancient Greek philosophy that teaches the practice of virtue as the only true good, and encourages focusing only on what lies within one's own control.","attribution":"Philosophy"},
+  {"category":"philosophy","content":"Existentialism explores questions about individual freedom, choice, and meaning, arguing that people must create their own purpose in a universe that does not provide one automatically.","attribution":"Philosophy"},
+  {"category":"philosophy","content":"The Socratic method uses a series of questions and answers to expose contradictions in a person's beliefs, encouraging deeper critical thinking rather than simply providing answers.","attribution":"Philosophy"},
+  {"category":"philosophy","content":"The impediment to action advances action. What stands in the way becomes the way.","attribution":"Marcus Aurelius, Meditations"},
+  {"category":"philosophy","content":"Every new beginning comes from some other beginning's end.","attribution":"Seneca, Letters from a Stoic"},
+  {"category":"philosophy","content":"Utilitarianism holds that the right action is the one that produces the greatest good for the greatest number of people, judging morality by outcomes rather than intentions.","attribution":"Philosophy"}
+]