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, 28 insertions, 0 deletions

diff --git a/data/packs/programming.json b/data/packs/programming.json
new file mode 100644
index 0000000..4384c6b
--- /dev/null
+++ b/data/packs/programming.json
@@ -0,0 +1,28 @@
+[
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"const total = items.reduce((acc, item) => acc + item.price, 0);"},
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"const unique = [...new Set(values)].sort((a, b) => a - b);"},
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"export async function load(url) { const res = await fetch(url); return res.json(); }"},
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"document.querySelectorAll('.row').forEach(el => el.classList.toggle('active'));"},
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"if (typeof value !== 'string' || value.length === 0) { return null; }"},
+  {"category":"programming","language":"javascript","attribution":"JavaScript","content":"const { id, name = 'anonymous', ...rest } = await request.json();"},
+  {"category":"programming","language":"python","attribution":"Python","content":"squares = [n * n for n in range(1, 21) if n % 3 != 0]"},
+  {"category":"programming","language":"python","attribution":"Python","content":"def fib(n): return n if n < 2 else fib(n - 1) + fib(n - 2)"},
+  {"category":"programming","language":"python","attribution":"Python","content":"with open('data.csv', encoding='utf-8') as f: rows = [line.split(',') for line in f]"},
+  {"category":"programming","language":"python","attribution":"Python","content":"counts = {word: text.count(word) for word in set(text.split())}"},
+  {"category":"programming","language":"python","attribution":"Python","content":"try: value = int(raw) except ValueError: value = 0"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"let mut counts: HashMap<String, usize> = HashMap::new();"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"fn main() { println!(\"{}\", args().skip(1).collect::<Vec<_>>().join(\" \")); }"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"let total: i64 = values.iter().filter(|v| **v > 0).sum();"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"match result { Ok(v) => println!(\"{v}\"), Err(e) => eprintln!(\"error: {e}\") }"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"pub struct Point { pub x: f64, pub y: f64 }"},
+  {"category":"programming","language":"rust","attribution":"Rust","content":"impl Display for Token { fn fmt(&self, f: &mut Formatter) -> Result { write!(f, \"{}\", self.0) } }"},
+  {"category":"programming","language":"clike","attribution":"C","content":"int *buf = malloc(len * sizeof(int)); if (!buf) return -1;"},
+  {"category":"programming","language":"clike","attribution":"C","content":"for (int i = 0; i < n; i++) { sum += a[i] * b[i]; }"},
+  {"category":"programming","language":"clike","attribution":"C","content":"struct node { int value; struct node *next; };"},
+  {"category":"programming","language":"clike","attribution":"Go","content":"for i, v := range items { fmt.Printf(\"%d: %v\\n\", i, v) }"},
+  {"category":"programming","language":"clike","attribution":"Go","content":"if err != nil { return fmt.Errorf(\"read config: %w\", err) }"},
+  {"category":"programming","language":"clike","attribution":"Java","content":"public static void main(String[] args) { System.out.println(\"ready\"); }"},
+  {"category":"programming","language":"shell","attribution":"Shell","content":"grep -rn \"TODO\" src/ | awk -F: '{print $1}' | sort -u"},
+  {"category":"programming","language":"shell","attribution":"Shell","content":"for f in *.log; do gzip -9 \"$f\" && echo \"packed $f\"; done"},
+  {"category":"programming","language":"shell","attribution":"Shell","content":"export PATH=\"$HOME/.local/bin:$PATH\" && command -v rg >/dev/null || echo missing"}
+]