Word Search bug-fixes + Codex polish

Two reported bugs, same root cause: the fixed-cell grid overflowed its wrapper
on Large, so (a) the last column spilled past the border and (b) the pointer→cell
math drifted across the row, recording finds "off by a letter".
* Grid now uses 1fr columns with max-width = n·32px: the board grows with the
  grid and can never overflow (shrinks to fit a narrow phone instead).
* cellAt() accounts for the grid padding/border, so selection is exact edge-to-edge.
* restore() now validates each saved find against the CURRENT grid and drops any
  whose cells no longer spell the word — clears stale highlights if the day's
  puzzle changed.

Codex follow-ups:
* _ws_propose now requires >= large.count + 4 valid words before accepting an LLM
  proposal (else falls back to a curated theme), so a thin LLM result can't
  underfill Large. Added a thin-LLM fallback test.
* Cleaned Svelte warnings: removed the now-unused .gamecard.soon CSS, added an
  ARIA role/label to the grid, declared gridEl with $state. Build is warning-clean.
* Added a stale-load guard in WordSearchGame.load() so rapid size switches can't
  let an older request overwrite the newer selection.

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

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

@@ -140,13 +140,10 @@
     box-shadow: var(--shadow); transition: border-color 0.14s ease, transform 0.14s ease;
   }
   .gamecard:hover { border-color: var(--accent); transform: translateY(-1px); }
-  .gamecard.soon { cursor: default; opacity: 0.6; box-shadow: none; }
-  .gamecard.soon:hover { border-color: var(--line); transform: none; }
   .gc-icon { font-size: 2rem; color: var(--accent); line-height: 1; flex-shrink: 0; }
   .gc-body h2 { font-size: 1.2rem; margin: 0 0 3px; }
   .gc-sub { color: var(--muted); font-size: 0.86rem; margin: 0 0 8px; }
   .gc-status { font-size: 0.84rem; color: var(--accent-deep); font-weight: 600; margin: 0; }
-  .gamecard.soon .gc-status { color: var(--muted); font-weight: 400; font-style: italic; }
 
   .variant { display: flex; gap: 10px; justify-content: center; margin: 0 0 22px; }
   .vchip {