Phase 12 + 13: collocation coach + vocabulary garden

Phase 12 — collocation coach: a third suggestion family for gentle
"natives usually say…" hints on non-native word pairings, reusing the
existing runPass/pendingScope/rail machinery.
- llm/collocation.go (RunCollocation, 25s floor, reuses ParseCheckpoint)
  + collocationSystemPrompt/CollocationMessages (warm, Mandarin gloss,
  defers grammar/spelling to the grammar family)
- migration 0005 rebuilds the suggestions table to extend the type CHECK
  (SQLite can't ALTER a CHECK)
- collocationScope + CollocationLimit + POST /{id}/collocation
- fix: grammarScope was `type != 'voice'` and would wipe the new
  collocation flags; now `type NOT IN ('voice','collocation')`
- frontend: --color-blossom, "Make it sound natural 🌸" pill,
  collocating/runCollocation in useCheckpoint, StatusBar dot

Phase 13 — vocabulary garden: capture looked-up words and surface them
for gentle spaced repetition.
- new internal/vocab package: migration 0006 (vocab_words, SM-2-lite
  columns, doc_id ON DELETE SET NULL, UNIQUE(user_id,word)),
  scheduler.go (Leitner ladder 1/3/7/16/35 then geometric; gentle
  "again", no streak-shaming), handlers (capture-upsert/list/due/
  review/delete, owner-scoped, SQLite-side datetime math)
- auto-capture on word lookup (dictionary-known words only, captures
  the surrounding sentence + doc_id) + 🤍/💚 toggle on WordCard
- GardenPanel: blossom grid (bloom by reps), flashcard review (sentence
  blanked, flip, again/good/easy, recognition↔production), sleepy-kitten
  footer; opened from a global 🌷 header button

Tests: TestCollocationPassCoexists, vocab scheduler + handlers, db CHECK
extended. go build/vet/test + tsc + vite + vitest (51/51) clean;
migration verified against a copy of the live DB; live backend smoke
walked the full vocab lifecycle + the warm-502 collocation path.

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

web/src/components/Editor/WordCard.tsx

@@ -11,11 +11,15 @@ interface Props {
   word: string
   info: WordInfo | null
   loading: boolean
+  // Whether the word is in the vocabulary garden (auto-saved on lookup). The
+  // heart toggles it; `onToggleSave` removes/re-adds it.
+  saved: boolean
+  onToggleSave: () => void
   style: React.CSSProperties
   onReplace: (synonym: string) => void
 }
 
-export function WordCard({ word, info, loading, style, onReplace }: Props) {
+export function WordCard({ word, info, loading, saved, onToggleSave, style, onReplace }: Props) {
   const definitions = info?.definitions ?? []
   const synonyms = info?.synonyms ?? []
   const gloss = info?.gloss ?? ''
@@ -48,18 +52,35 @@ export function WordCard({ word, info, loading, style, onReplace }: Props) {
         <span className="font-bold" style={{ color: 'var(--color-plum)' }}>
           {word}
         </span>
-        {speechSupported() && (
-          <button
-            type="button"
-            onClick={() => speak(word)}
-            aria-label={`Pronounce ${word}`}
-            title="朗读 · Read aloud"
-            className="ml-auto flex h-7 w-7 items-center justify-center rounded-full text-sm"
-            style={{ background: 'var(--color-surface-alt)', color: 'var(--color-plum)' }}
-          >
-            🔊
-          </button>
-        )}
+        <div className="ml-auto flex items-center gap-1.5">
+          {!empty && !loading && (
+            <button
+              type="button"
+              onClick={onToggleSave}
+              aria-label={saved ? 'Remove from vocabulary garden' : 'Save to vocabulary garden'}
+              aria-pressed={saved}
+              title={saved ? '已在词汇花园 · In your garden (tap to remove)' : '加入词汇花园 · Save to garden'}
+              className="flex h-7 w-7 items-center justify-center rounded-full text-sm transition-transform"
+              style={{
+                background: saved ? 'var(--color-accent)' : 'var(--color-surface-alt)',
+              }}
+            >
+              {saved ? '💚' : '🤍'}
+            </button>
+          )}
+          {speechSupported() && (
+            <button
+              type="button"
+              onClick={() => speak(word)}
+              aria-label={`Pronounce ${word}`}
+              title="朗读 · Read aloud"
+              className="flex h-7 w-7 items-center justify-center rounded-full text-sm"
+              style={{ background: 'var(--color-surface-alt)', color: 'var(--color-plum)' }}
+            >
+              🔊
+            </button>
+          )}
+        </div>
       </div>
 
       {/* How to say it — the pronunciation aid for an English learner, paired