Remove the title field — a note is named by its first line

Operator (note 2897): "notes shouldn't have a title field." The concept of a NAME
stays — search results, export filenames and the command palette all need one —
but nothing is typed into it any more. `display_title` is now the first non-empty
line of the body, falling back to the first checklist item.

That fallback is what step 2 bought, and the reason this could not go first: a
checklist had no body to be named from, so the title was its only name. Now every
note has a body, and a note that is only a checklist is named by its first item.

Gone everywhere: the column and note_revisions.title (0026), the field on the
core's Note/NoteCreateInput/NoteRevision and its SQLite columns (user_version 7),
`normalize_title`, the wire field, the FFI record and `NoteEdit::Title` /
`ClearTitle`, the web editor's "Title (optional)" input and the card's <h3>, and
the Android title field in both the compose sheet and the editor.

**The search vector had to be rebuilt, not just left alone.** `notes.search_vector`
is a STORED GENERATED column whose expression names `title` — Postgres refuses to
drop a column another generated column depends on. It is dropped and recreated over
`display_title` at weight A, which keeps the original intent: a note's NAME ranks
above the rest of its body.

**An imported title becomes the note's first body line.** Keep notes carry one, and
so does any ThoughtSync export taken before this. Dropping it would silently lose
text someone wrote; folding it in puts it exactly where a name now lives, so the
note arrives named as it was. Skipped when the body already opens with that line,
so re-importing an export this code produced doesn't stack duplicates.

Two smaller things fell out. The Android editor loses its bold first field — one
weight throughout, because the first line is the note's name but not a different
KIND of text, which is most of step 4 arriving early. And `ClearTitle`'s
justification comment moved to `ClearRemindAt`, which is now the surviving example
of why NoteEdit is a list rather than a struct of options.

Protocol note corrected to say what actually shipped: v2 is "no kind, no title",
one bump for the pair.

Verified with the local Rust gate this time, not by CI: fmt, clippy and 116 tests
all green before pushing. It caught four things — orphaned serde attributes where
fields were removed, a `wire::Preview.title` I deleted by mistake (a link preview
still has one), nine retention fixtures inserting a dropped column, and four
rustfmt diffs.

frontend/src/stores/notes.ts

@@ -52,19 +52,17 @@ export interface LinkPreview {
   site_name: string | null;
 }
 
-// A past version of a note's title+body (version history).
+// A past version of a note's 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;
-  // The note's display NAME: explicit title, else its first body line (server-derived).
-  // Every note has one, so a body-only note still has something to be called.
+  // The note's NAME: its first body line, else its first checklist item
+  // (server-derived). Every note has one, so every note has something to be called.
   display_title: string;
   body: string;
   color: NoteColor;
@@ -134,10 +132,9 @@ export const useNotesStore = defineStore("notes", () => {
   }
 
   async function create(input: {
-    title: string;
     body: string;
     color: NoteColor;
-      items?: string[];
+    items?: string[];
   }): Promise<Note> {
     const note = await repo.notes.create(input);
     reconcile(note);
@@ -147,7 +144,7 @@ export const useNotesStore = defineStore("notes", () => {
   async function mutate(
     id: string,
     changes: Partial<
-      Pick<Note, "title" | "body" | "color" | "pinned" | "archived" | "remind_at" | "recurrence">
+      Pick<Note, "body" | "color" | "pinned" | "archived" | "remind_at" | "recurrence">
     >,
   ): Promise<void> {
     reconcile(await repo.notes.update(id, changes));