Code-review fixes for collocation coach + vocab garden

Correctness:
- useCheckpoint: clear the busy flag unconditionally so overlapping
  explicit passes don't strand each other's spinner; explicit actions
  now also supersede a queued auto-check and clear the stranded
  "checking" dot. Deduped runVoice/runCollocation into runExplicitPass.
- EditorCore: token-guard the auto-capture so a late capture can't
  resurrect a removed word; move toggleSaveWord side effects out of the
  setWordInfo updater (StrictMode double-fire); fix sentenceAround offset
  desync via shared exampleAt (textBetween + parentOffset, single resolve);
  optimistic saved state so the heart doesn't flash unsaved.
- vocab capture: normalize word to lower+trim (matches lexicon) so
  "Apple"/"apple" don't make duplicate cards; check rows.Err() in queryList.
- GardenPanel: Promise.allSettled so a /due failure doesn't blank the
  whole garden; scrim click during review ends the review (mirrors Esc);
  gate footer on !error; O(1) due lookup via a Set.

Features requested in review:
- Definition-only review card: add vocab_words.definition (migration
  0007) as an English fallback meaning, threaded through capture and used
  by review/garden when there's no Chinese gloss.
- Scheduler caps: maxEase 3.0 + maxInterval 365d so "easy" growth can't
  push a word out of rotation for years.

Tests: TestCaptureCaseInsensitive, TestCaptureStoresDefinitionFallback,
TestCapsBoundGrowth. go build/vet/test, tsc, vitest 51/51, vite build clean.

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

internal/vocab/scheduler.go

@@ -23,10 +23,17 @@ var ladder = []int{1, 3, 7, 16, 35}
 
 const (
 	minEase        = 1.3
+	maxEase        = 3.0  // ease ceiling — keeps "easy" from compounding growth without bound
 	startEase      = 2.5
 	easyBonus      = 1.3   // multiplier applied on top of a "good" step for "easy"
 	easeAgainDelta = -0.20 // ease nudged down on a lapse (still floored at minEase)
 	easeEasyDelta  = 0.15  // ease nudged up when a card feels easy
+
+	// maxInterval caps how far a card can drift into the future. Even a word
+	// graded "easy" many times resurfaces about once a year, so nothing silently
+	// leaves the garden forever (the whole point is to keep words in gentle
+	// rotation, not to retire them).
+	maxInterval = 365
 )
 
 // State is the spaced-repetition state of one card. It mirrors the scheduling
@@ -61,7 +68,7 @@ func (s State) next(grade Grade) State {
 		reps := s.Reps + 1
 		return State{
 			Reps:     reps,
-			Interval: int(math.Round(float64(goodInterval(reps, s.Interval, ease)) * easyBonus)),
+			Interval: clampInterval(int(math.Round(float64(goodInterval(reps, s.Interval, ease)) * easyBonus))),
 			Ease:     ease,
 			Lapses:   s.Lapses,
 		}
@@ -69,7 +76,7 @@ func (s State) next(grade Grade) State {
 		reps := s.Reps + 1
 		return State{
 			Reps:     reps,
-			Interval: goodInterval(reps, s.Interval, ease),
+			Interval: clampInterval(goodInterval(reps, s.Interval, ease)),
 			Ease:     ease,
 			Lapses:   s.Lapses,
 		}
@@ -93,5 +100,15 @@ func clampEase(e float64) float64 {
 	if e < minEase {
 		return minEase
 	}
+	if e > maxEase {
+		return maxEase
+	}
 	return e
 }
+
+func clampInterval(d int) int {
+	if d > maxInterval {
+		return maxInterval
+	}
+	return d
+}