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, 56 insertions, 0 deletions

diff --git a/web/src/pb.js b/web/src/pb.js
new file mode 100644
index 0000000..cd4413c
--- /dev/null
+++ b/web/src/pb.js
@@ -0,0 +1,56 @@
+const STORAGE_KEY = 'typerpunk:pb';
+
+function load() {
+    try {
+        const raw = JSON.parse(localStorage.getItem(STORAGE_KEY));
+        return raw && typeof raw === 'object' ? raw : {};
+    } catch {
+        return {};
+    }
+}
+
+export function getPersonalBest(modeKey) {
+    if (!modeKey) return null;
+    return load()[modeKey] || null;
+}
+
+// All recorded bests, best-WPM first, for a full stats/profile view rather
+// than a single mode's lookup.
+export function getAllPersonalBests() {
+    const all = load();
+    return Object.entries(all)
+        .map(([modeKey, record]) => ({ modeKey, ...record }))
+        .sort((a, b) => b.wpm - a.wpm);
+}
+
+// Reconciles local bests with the server's on sign-in - takes max(local,
+// remote) per mode rather than overwriting, so a best set on this device
+// before ever signing in isn't lost just because the server hadn't seen it
+// yet. Guests never call this; the account has to exist first.
+export function mergeRemoteBests(remoteBests) {
+    if (!Array.isArray(remoteBests) || remoteBests.length === 0) return;
+    const all = load();
+    for (const { mode_key: modeKey, wpm, date } of remoteBests) {
+        const local = all[modeKey];
+        if (!local || wpm > local.wpm) {
+            all[modeKey] = { wpm, date: date ? Date.parse(date) || Date.now() : Date.now() };
+        }
+    }
+    try { localStorage.setItem(STORAGE_KEY, JSON.stringify(all)); } catch {}
+}
+
+// Records a finished test's WPM against its mode's best, updating storage
+// only when it's actually a new best. Returns the previous best (or null)
+// and whether this run just beat it, so the end screen can show both in one
+// read without a separate lookup.
+export function recordResult(modeKey, wpm) {
+    if (!modeKey) return { isNewBest: false, previous: null };
+    const all = load();
+    const previous = all[modeKey] || null;
+    const isNewBest = !previous || wpm > previous.wpm;
+    if (isNewBest) {
+        all[modeKey] = { wpm, date: Date.now() };
+        try { localStorage.setItem(STORAGE_KEY, JSON.stringify(all)); } catch {}
+    }
+    return { isNewBest, previous: previous ? previous.wpm : null };
+}