M6: version history — note revisions + restore

A note's title+body is snapshotted on each edit that changes either, so an accidental overwrite can be viewed and restored (task 1906). Underwrites 'dump freely, nothing is lost'.

Backend: note_revisions table (migration 0014) + NoteRevision model; update_note records a revision of the PRE-edit state whenever title/body changes; GET /api/notes/<id>/revisions (newest 50) and POST /api/notes/<id>/revisions/<rev_id>/restore (snapshots the current state first so restore is itself undoable, then applies the revision with the usual title/body ripple — display name, links, #tags, backlinks). Title+body only in v1.

Frontend: a History toggle in the modal editor opens a panel of past versions (timestamp + preview) with per-row Restore. Store gains fetchRevisions/restoreRevision.

Migration 0014 runs on deploy; DB behavior operator-verified (no Postgres CI lane).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/stores/notes.ts

@@ -29,6 +29,14 @@ export interface Attachment {
   mime: string;
 }
 
+// A past version of a note's title+body (version history).
+export interface NoteRevision {
+  id: string;
+  title: string | null;
+  body: string;
+  created_at: string | null;
+}
+
 export interface Note {
   id: string;
   title: string | null;
@@ -204,6 +212,17 @@ export const useNotesStore = defineStore("notes", () => {
     if (idx >= 0) items.value.splice(idx, 1);
   }
 
+  async function fetchRevisions(id: string): Promise<NoteRevision[]> {
+    const res = await api.get<{ revisions: NoteRevision[] }>(`/api/notes/${id}/revisions`);
+    return res.revisions;
+  }
+
+  async function restoreRevision(id: string, revId: string): Promise<Note> {
+    const note = await api.post<Note>(`/api/notes/${id}/revisions/${revId}/restore`);
+    reconcile(note);
+    return note;
+  }
+
   return {
     items,
     loading,
@@ -229,5 +248,7 @@ export const useNotesStore = defineStore("notes", () => {
     trash,
     restore,
     deleteForever,
+    fetchRevisions,
+    restoreRevision,
   };
 });