Word Search polish: constant cell size, 28-word themes, per-size variety, palette

Playtesting fixes:
* Constant cell size (~32px) — the board GROWS with the grid instead of shrinking
  letters into a fixed box. Fixes Small's oversized spacing; on a narrow phone the
  largest grid gently scales to fit (the standard word-search compromise).
* Themes now gather ~28 words (LLM asked for 28; curated fallbacks ~22 each), and
  each size samples its OWN subset — so every tier is a distinct puzzle. Large is
  now reliably full (14 words on 14×14), fixing the "13 words / 11 listed" mismatch.
* Tiers: small 8×8/6, med 11×11/10, large 14×14/14.
* Word list is now a framed "Find these · n/total" palette panel (pill chips that
  take on each found word's colour) instead of loose text under the grid.
* Size chips use qualitative labels (cosy / balanced / a longer sit) so no count
  can ever contradict the actual puzzle.

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

frontend/src/routes/play/+page.svelte

@@ -113,9 +113,9 @@
     <WordGame {variant} onstatus={refreshStatus} />
   {:else if view === 'wordsearch'}
     <div class="variant">
-      <button class="vchip" class:on={wsSize === 'small'} onclick={() => (wsSize = 'small')}>Small<span>cosy · 6 words</span></button>
-      <button class="vchip" class:on={wsSize === 'med'} onclick={() => (wsSize = 'med')}>Medium<span>9 words</span></button>
-      <button class="vchip" class:on={wsSize === 'large'} onclick={() => (wsSize = 'large')}>Large<span>a longer sit · 13 words</span></button>
+      <button class="vchip" class:on={wsSize === 'small'} onclick={() => (wsSize = 'small')}>Small<span>cosy</span></button>
+      <button class="vchip" class:on={wsSize === 'med'} onclick={() => (wsSize = 'med')}>Medium<span>balanced</span></button>
+      <button class="vchip" class:on={wsSize === 'large'} onclick={() => (wsSize = 'large')}>Large<span>a longer sit</span></button>
     </div>
     <WordSearchGame size={wsSize} onstatus={refreshStatus} />
   {/if}