notes: color leaves the model, the wire and all three surfaces

Step 3 of M315, and the destructive half. Steps 1 and 2 stopped every read of
this field: a card is one neutral surface per theme, and the only coloured
thing on a board is a tag. What was left was a column written by a picker and
read by nothing.

Rule 22 — the old path comes out completely. No flag, no fallback, no
"override if set".

Server: the column, the `?color=` facet, the create/update/serialise paths,
the sync assignment, the front-matter line, and Keep's colour map. Alembic
0029 drops it and sweeps `"color"` out of stored saved-filter params — a view
that silently filtered on a field the app no longer has would return nothing
and never say why. That sweep is Python, not `params::jsonb - 'color'`,
because Postgres has no try-cast and one malformed blob would abort a
migration that is running over somebody's saved views.

`NOTE_COLORS` moves from `models/note.py` to `colors.py`. A palette defined on
the model that lost one is an invitation to put the column back; labels still
name a colour, so the vocabulary belongs where the normalizer already is.

Core: the field, the facet, the `NoteCreateInput`, and every read and write in
store/push/pull. Local schema v9 drops the column and does the same
saved-filter sweep, guarded on `json_valid` so a corrupt blob loses a key
rather than becoming NULL. The uniffi layer drops `NoteEdit::Color` and
`NoteDraft.color` with it.

Web: `ColorPicker.vue`, the per-card swatch popover and its stylesheet rule,
the FilterBar colour row, the facet in the query round-trip, and the colour
half of the editor's baseline-and-save. Android: the `ColorSheet`, the
`Picker.COLOR` case, the toolbar's swatch dot, `EditorAction.SetColor`.

## The protocol: v4, and the floor deliberately stays at 3

Checked against `compat.rs` and the push handler rather than trusting the
`#[serde(default)]` annotation, because the v2 precedent points the other way:
v2 dropped `kind` and `title` and DID raise both floors, on the rule that
dropping a field a client sends and expects back is breaking.

`color` fails the second half of that test. A v3 client reading a v4 note gets
`"default"` from its own serde default and draws the colour it derives
locally — the board it drew yesterday. A v3 client pushing `color` has the key
ignored, since `_assign_note_fields` reads its payload key by key and never
validates the shape. Neither direction errors and neither shows anything
wrong. `title` was the note's NAME; this is a field that no longer renders.

So `SYNC_PROTOCOL_VERSION` and `CLIENT_PROTOCOL_VERSION` go to 4, and both
floors stay at 3. `docs/sync.md` carries the reasoning and the per-version
history, and its push example is brought back in line — it still listed
`title`, `kind` and `items`, all gone before this.

Import stays tolerant: a pre-M315 export or a Keep takeout carrying `color:`
imports fine, the key simply read past. Old exports must still import.

#3041

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/adapters/repo.ts

@@ -9,7 +9,6 @@
 // consume. Client-side logic (list reconciliation, optimistic updates, toasts)
 // stays in the stores — the repo is data access only.
 
-import type { NoteColor } from "../notes/colors";
 import type { Note, NoteFacets, NoteView, NoteRevision } from "../stores/notes";
 import type { Label } from "../stores/labels";
 import type { SavedFilter } from "../stores/savedFilters";
@@ -33,13 +32,12 @@ export interface NoteListQuery {
 
 export interface NoteCreateInput {
   body: string;
-  color: NoteColor;
   items?: string[];
 }
 
 // The mutable subset of a note (PATCH /api/notes/:id).
 export type NoteChanges = Partial<
-  Pick<Note, "body" | "color" | "pinned" | "archived" | "remind_at" | "recurrence">
+  Pick<Note, "body" | "pinned" | "archived" | "remind_at" | "recurrence">
 >;
 
 export interface ChecklistItemChanges {

frontend/src/adapters/rest.ts

@@ -31,7 +31,6 @@ function notesQuery(q: NoteListQuery): string {
   if (q.labelId) params.append("label", q.labelId);
   for (const id of q.facets?.label ?? []) if (id) params.append("label", id);
   if (q.facets?.q) params.set("q", q.facets.q);
-  if (q.facets?.color) params.set("color", q.facets.color);
   if (q.facets?.has_reminder) params.set("has_reminder", "true");
   if (q.facets?.has_attachment) params.set("has_attachment", "true");
   if (q.facets?.created_after) params.set("created_after", q.facets.created_after);