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/sync.py

@@ -55,13 +55,12 @@ MAX_PUSH = 1000  # per-batch change cap
 # Bump SYNC_PROTOCOL_VERSION for ANY wire change. Raise
 # MIN_CLIENT_PROTOCOL_VERSION only for a genuinely BREAKING one: it is the switch
 # that hard-blocks older clients, so additive changes must leave it alone.
-# v2 (M13): `kind` left the wire. Dropping a field a v1 client sends and expects back
-# is breaking, so the FLOOR moves too — a v1 client would keep pushing a `kind` the
-# server no longer stores, and would read back notes without one.
+# v2 (M13): `kind` and `title` both left the wire. Dropping a field a v1 client sends
+# and expects back is breaking, so the FLOOR moves too — a v1 client would keep pushing
+# both and would read back notes carrying neither.
 #
-# `title` goes the same way in step 3. It lands in this same protocol generation, so
-# it needs no further bump — v2 means "no kind, no title", and nothing has run against
-# a half-applied v2.
+# One bump for the pair: they landed in the same protocol generation, and nothing ever
+# ran against a half-applied v2.
 SYNC_PROTOCOL_VERSION = 2
 MIN_CLIENT_PROTOCOL_VERSION = 2
 
@@ -197,8 +196,6 @@ def client_wins(client_edited_at: datetime | None, server_edited_at: datetime |
 def _assign_note_fields(note: Note, ch: dict) -> None:
     """Overwrite a note's scalar fields from a client's FULL-state change (sync is
     whole-note, not a partial patch — the client sends its authoritative version)."""
-    title = ch.get("title")
-    note.title = (title or "").strip() or None if isinstance(title, str) else None
     note.body = ch["body"] if isinstance(ch.get("body"), str) else ""
     note.color = normalize_color(ch.get("color"))
     note.pinned = bool(ch.get("pinned"))
@@ -214,6 +211,24 @@ def _assign_note_fields(note: Note, ch: dict) -> None:
         note.position = ch["position"]
 
 
+def _first_item_text(ch: dict) -> str:
+    """The first non-blank checklist item in a pushed change, or "".
+
+    Read straight from the payload rather than the database because the note's name is
+    computed BEFORE `_apply_note_items` has written anything — and a note whose body is
+    empty is named by its first item (M13 step 3).
+    """
+    items = ch.get("items")
+    if not isinstance(items, list):
+        return ""
+    for it in items:
+        if isinstance(it, dict):
+            text = (it.get("text") or "").strip()
+            if text:
+                return text
+    return ""
+
+
 async def _apply_note_items(db, note: Note, ch: dict) -> None:
     """Replace the note's checklist items with the client's (items sync inline).
 
@@ -296,14 +311,14 @@ async def _apply_note(db, ch: dict) -> dict:
     elif note.purged_at is not None:
         note.purged_at = None  # client re-created/edited → clear the tombstone
 
-    old_title, old_body = note.title, note.body
+    old_body = note.body
     _assign_note_fields(note, ch)
-    note.display_title = derive_display_title(note.title, note.body)
+    note.display_title = derive_display_title(note.body, _first_item_text(ch))
     if edited_at is not None:
         note.updated_at = edited_at
-    # Non-destructive LWW: snapshot the overwritten server title+body into history.
-    if not creating and (note.title != old_title or note.body != old_body):
-        db.add(NoteRevision(note_id=note.id, title=old_title, body=old_body))
+    # Non-destructive LWW: snapshot the overwritten server body into history.
+    if not creating and note.body != old_body:
+        db.add(NoteRevision(note_id=note.id, body=old_body))
     await db.flush()  # assign note.id before items/labels/links
     await _apply_note_items(db, note, ch)
     await _reconcile_tags(db, note)