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/business.json b/data/packs/business.json
new file mode 100644
index 0000000..627c6f0
--- /dev/null
+++ b/data/packs/business.json
@@ -0,0 +1,17 @@
+[
+  {"category":"business","content":"Price is what you pay, and value is what you get.","attribution":"Warren Buffett"},
+  {"category":"business","content":"The purpose of a business is to create and keep a customer.","attribution":"Peter Drucker"},
+  {"category":"business","content":"Henry Ford, founder of the Ford Motor Company, is credited with popularizing the moving assembly line, which dramatically reduced the time needed to build an automobile.","attribution":"History of Business"},
+  {"category":"business","content":"A balance sheet summarizes what a company owns and owes at a single point in time, split into assets, liabilities, and shareholders' equity.","attribution":"Business"},
+  {"category":"business","content":"Supply and demand describes how the price of a good tends to rise when demand exceeds supply, and fall when supply exceeds demand.","attribution":"Business"},
+  {"category":"business","content":"A startup's burn rate measures how quickly it spends its available cash, an important number for founders trying to plan how long the company can operate before running out of money.","attribution":"Business"},
+  {"category":"business","content":"Diversification spreads investment risk across different assets, so that a poor outcome in one area does not sink an entire portfolio.","attribution":"Business"},
+  {"category":"business","content":"Branding is the practice of shaping how customers perceive a company, going beyond a logo to include tone, values, and the overall experience of using a product.","attribution":"Business"},
+  {"category":"business","content":"A merger combines two companies into one, while an acquisition occurs when one company purchases and absorbs another, though the two terms are often used loosely in everyday conversation.","attribution":"Business"},
+  {"category":"business","content":"Cash flow tracks the actual movement of money into and out of a business, which can differ significantly from reported profit due to timing differences in payments.","attribution":"Business"},
+  {"category":"business","content":"The man who dies rich, dies disgraced.","attribution":"Andrew Carnegie"},
+  {"category":"business","content":"Market research helps a business understand its customers' needs and preferences before committing resources to a new product or service.","attribution":"Business"},
+  {"category":"business","content":"A monopoly exists when a single company dominates an entire market with no significant competition, often leading regulators to intervene to protect consumers.","attribution":"Business"},
+  {"category":"business","content":"Return on investment measures the profitability of an investment relative to its cost, expressed as a percentage to make it easy to compare different opportunities.","attribution":"Business"},
+  {"category":"business","content":"Customer obsession, rather than competitor focus, is the surest path to long term success.","attribution":"Jeff Bezos"}
+]