Play hub + Daily Word game (Phase 1 of the games feature)

A calm /play space — "after the brief, a small thing to enjoy." Framework-ready
for more games (Word Search next; zen/coloring later).

* Daily Word (5 letters / 6 guesses) + Long Word (6 / 7) — same Wordle mechanic,
  Upbeat Bytes flavor (no "Wordle" in the UI). Hopeful answers; after solving, a
  one-line "why this word matters."
* LLM proposes, code disposes: answers are picked deterministically by date-seed
  from a hand-curated hopeful pool that's pre-validated ⊆ the guess dictionary
  (always typeable), avoiding recent repeats; the LLM only adds the optional
  "why" (with fallback). daily_puzzles(date, game, variant, payload) stores them
  so everyone gets the same daily; the cycle pre-generates with the "why".
* Bundled guess dictionaries (words-5/6.json, ~12.6k/22.4k) for client-side guess
  validation — never the LLM. Answer lightly obfuscated (base64) in the payload.
* Private, gentle stats (played/solved/streak, guess distribution); spoiler-free
  emoji-grid share. No leaderboard, no timer, no streak-loss drama.
* Play in the bottom nav (replacing Browse, still on the lane rail) + the header.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/Header.svelte

@@ -11,6 +11,10 @@
     </a>
 
     <nav class="utils" aria-label="Your controls">
+      <a class="util desk" href="/play" title="Play — daily puzzles">
+        <svg viewBox="0 0 24 24" aria-hidden="true"><rect x="4" y="4" width="7" height="7" rx="2" fill="none" stroke="currentColor" stroke-width="1.8"/><rect x="13" y="4" width="7" height="7" rx="2" fill="none" stroke="currentColor" stroke-width="1.8"/><rect x="4" y="13" width="7" height="7" rx="2" fill="none" stroke="currentColor" stroke-width="1.8"/><rect x="13" y="13" width="7" height="7" rx="2" fill="none" stroke="currentColor" stroke-width="1.8"/></svg>
+        <span>Play</span>
+      </a>
       {#if user}
         <button class="util desk" onclick={onSaved} title="Saved articles">
           <svg viewBox="0 0 24 24" aria-hidden="true"><path d="M6 3h12v18l-6-4-6 4z"