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

internal/llm/collocation.go

@@ -0,0 +1,35 @@
+package llm
+
+import (
+	"context"
+	"time"
+)
+
+// CollocationInterval is the minimum gap between collocation passes for one
+// document. Like the voice pass it runs on an explicit user action ("Make it
+// sound natural") rather than a typing cadence, so this floor only guards the
+// inference endpoint against the button being mashed.
+const CollocationInterval = 25 * time.Second
+
+// RunCollocation sends the WHOLE document for a collocation pass — gentle
+// "natives usually say…" hints on non-native word pairings — and parses the JSON
+// result with the checkpoint's tolerant parser. It is deliberately NOT
+// TruncateDoc'd: like the voice pass it reads the whole document so the hints
+// reflect the full piece. Each flag carries a native replacement to apply.
+//
+// The tone argument is accepted for a uniform pass signature and passed through
+// to the prompt so a hint can prefer a register-appropriate pairing.
+func RunCollocation(ctx context.Context, client LLMClient, contentText, tone string) ([]RawSuggestion, error) {
+	raw, err := client.Complete(ctx, CompletionRequest{
+		Messages:          CollocationMessages(contentText, tone),
+		MaxTokens:         2048,
+		Temperature:       0.3,
+		RepetitionPenalty: 1.15,
+		TopP:              0.9,
+		Stop:              []string{"```", "\n\n\n\n"},
+	})
+	if err != nil {
+		return nil, err
+	}
+	return ParseCheckpoint(raw)
+}