Finish Phase 22: the half of Petal that works with the tunnel down

Grammar lite, the false-friend list, the daily invitation and the offline
miscollocations — the four remaining §5–§6 items, all client-side and all
alive on a box that cannot reach the model.

The offline collocations forced a schema change. `type` had been doubling
as the answer to "which engine found this" — `mechanics` meant offline —
and that stops being true the moment an offline rule proposes a
collocation. Migration 0013 adds `source` (llm | local) and every pass now
scopes its DELETE by engine; without it the coach silently wiped every
offline chunk on the page. Existing rows backfill by type, so a pre-0013
collocation row is claimed as the coach's, which it was: the offline list
did not exist yet.

The rule pack is hand-curated rather than mined, and the entries left out
are the point — `married with` is wrong until "married with children",
`arrive to` wants at or in depending on the noun. A pack running on every
keystroke must not correct correct writing.

Claude-Session: https://claude.ai/code/session_016y6gyuHkQXPiEuW8RGQyua

internal/db/models.go

@@ -106,7 +106,11 @@ type Suggestion struct {
 	Explanation string    `json:"explanation"`
 	Type        string    `json:"type"`   // grammar | phrasing | idiom | clarity | voice | collocation
 	Status      string    `json:"status"` // pending | accepted | rejected
-	CreatedAt   time.Time `json:"created_at"`
+	// Source names the engine that proposed the edit, not its family: an offline
+	// rule and the model can both propose a collocation, and the writer is never
+	// told which one spoke. It exists so each pass can replace its own rows.
+	Source    string    `json:"source"` // llm | local
+	CreatedAt time.Time `json:"created_at"`
 }
 
 // Suggestion type and status values, mirrored from the schema CHECK constraints.
@@ -119,6 +123,12 @@ const (
 	SuggestionTypeCollocation = "collocation"
 	SuggestionTypeMechanics   = "mechanics" // deterministic rule-based pass (no LLM)
 
+	// Who proposed it. The offline rule pack ('local') runs on every edit inside
+	// the browser and survives a VPN-down box; the model ('llm') adds the long
+	// tail when it is reachable.
+	SuggestionSourceLLM   = "llm"
+	SuggestionSourceLocal = "local"
+
 	SuggestionStatusPending  = "pending"
 	SuggestionStatusAccepted = "accepted"
 	SuggestionStatusRejected = "rejected"