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.

src/thoughtsync/notes/import_export.py

@@ -36,8 +36,6 @@ def _note_markdown(note: Note, labels: list, items: list) -> str:
     """One note as a human-readable Markdown file with a small frontmatter block.
     The authoritative machine format is notes.json; this is for reading/portability."""
     fm = ["---"]
-    if note.title:
-        fm.append(f"title: {note.title}")
     fm.append(f"display_name: {note.display_title}")
     if labels:
         fm.append("labels: [" + ", ".join(lb["name"] for lb in labels) + "]")
@@ -276,19 +274,29 @@ async def _create_imported_note(
     db, owner_id, spec: dict, zf: zipfile.ZipFile, position: int, budget: _ImportBudget
 ) -> bool:
     """Insert one imported note plus its items/labels/attachments, reusing the same
-    display-title derivation + tag/link reconciliation as create_note. Returns False
-    (nothing written) when the spec is empty."""
-    title = (spec.get("title") or "").strip() or None
+    name derivation + tag reconciliation as create_note. Returns False (nothing
+    written) when the spec is empty."""
     body = spec.get("body") or ""
+    # An imported title becomes the note's FIRST BODY LINE.
+    #
+    # ThoughtSync has no title field any more (M13 step 3), but the things people
+    # import from do — Keep notes carry one, and so does any export taken before this.
+    # Dropping it would silently lose text someone wrote; folding it into the body puts
+    # it exactly where a name now lives, so the note comes in named the way it was.
+    # Skipped when the body already opens with that line, so re-importing an export
+    # this code produced doesn't stack duplicates.
+    title = (spec.get("title") or "").strip()
+    if title and body.lstrip().split("\n", 1)[0].strip() != title:
+        body = f"{title}\n{body}" if body.strip() else title
+
     items = spec.get("items") or []
-    has_items = any((it.get("text") or "").strip() for it in items)
-    if is_empty_note(title, body) and not has_items:
+    item_texts = [t for t in ((it.get("text") or "").strip() for it in items) if t]
+    if is_empty_note(body, item_texts):
         return False
 
     note = Note(
         owner_id=owner_id,
-        title=title,
-        display_title=derive_display_title(title, body),
+        display_title=derive_display_title(body, item_texts[0] if item_texts else None),
         body=body,
         color=normalize_color(spec.get("color")),
         pinned=bool(spec.get("pinned")),