M3 wiki-links: [[links]] + backlinks

- Migration 0009: note_links (source_id, target_norm). Parse [[...]] from body on
  create/update and rewrite the source's links. GET /api/notes/titles (owner
  {id,title} index for client-side resolution); GET /api/notes/<id>/backlinks.
- Frontend: titles store; LinkedText renders [[Title]] styled on cards; editor
  shows Links (outgoing, resolve/create-on-click) + Linked-from (backlinks),
  clicking navigates the editor to the target note (board + search).
- notes store: fetchOne, createTitled. DB-free link-parser tests.

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

frontend/src/stores/titles.ts

@@ -0,0 +1,33 @@
+import { defineStore } from "pinia";
+import { ref } from "vue";
+import { api } from "../api/client";
+
+export interface TitleEntry {
+  id: string;
+  title: string;
+}
+
+// Owner's {id,title} index, used to resolve [[wiki-links]] client-side.
+export const useTitlesStore = defineStore("titles", () => {
+  const items = ref<TitleEntry[]>([]);
+  const loaded = ref(false);
+
+  async function load(): Promise<void> {
+    if (loaded.value) return;
+    const res = await api.get<{ titles: TitleEntry[] }>("/api/notes/titles");
+    items.value = res.titles;
+    loaded.value = true;
+  }
+
+  async function reload(): Promise<void> {
+    loaded.value = false;
+    await load();
+  }
+
+  function resolve(title: string): TitleEntry | null {
+    const norm = title.trim().toLowerCase();
+    return items.value.find((t) => t.title.trim().toLowerCase() === norm) ?? null;
+  }
+
+  return { items, loaded, load, reload, resolve };
+});