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/components/NoteEditor.vue

@@ -1,7 +1,6 @@
 <script setup lang="ts">
 import { computed, nextTick, onMounted, ref, watch } from "vue";
 import { useNotesStore } from "../stores/notes";
-import ColorPicker from "./ColorPicker.vue";
 import Icon from "./Icon.vue";
 import LabelPicker from "./LabelPicker.vue";
 import LinkPreview from "./LinkPreview.vue";
@@ -9,7 +8,7 @@ import { fromLocalInput, toLocalInput } from "../notes/datetime";
 import { takeMorphOrigin } from "../composables/useEditorMorph";
 import { prefersReducedMotion } from "../composables/useReducedMotion";
 import type { Note, NoteLabel, NoteRevision } from "../stores/notes";
-import { labelChipClasses, type NoteColor } from "../notes/colors";
+import { labelChipClasses } from "../notes/colors";
 import {
   afterEnter,
   type EditorBlock,
@@ -41,7 +40,6 @@ const body = computed(() => joinBlocks(blocks.value));
 function setBody(text: string): void {
   blocks.value = splitBlocks(text);
 }
-const color = ref<NoteColor>(props.note?.color ?? "default");
 const labelList = ref<NoteLabel[]>(props.note ? [...props.note.labels] : []);
 // Whether this editor is showing the checklist. A note HAS a checklist (M13 step 2)
 // rather than BEING one, so this is a view flag, not a property of the note: it turns
@@ -80,10 +78,7 @@ const fileInput = ref<HTMLInputElement | null>(null);
 const uploadError = ref("");
 
 // Baseline for edit-mode change detection (save only when text actually changed).
-const baseline = ref<{ body: string; color: NoteColor }>({
-  body: props.note?.body ?? "",
-  color: (props.note?.color ?? "default") as NoteColor,
-});
+const baseline = ref<{ body: string }>({ body: props.note?.body ?? "" });
 
 const isCreate = computed(() => noteId.value === null);
 const hasContent = computed(() => body.value.trim() !== "");
@@ -96,7 +91,6 @@ const draftNote = computed<Note>(() => ({
   id: "",
   display_title: "",
   body: body.value,
-  color: color.value,
   position: 0,
   pinned: false,
   archived: false,
@@ -124,17 +118,16 @@ watch(
   (n) => {
     noteId.value = n?.id ?? null;
     setBody(n?.body ?? "");
-    color.value = (n?.color ?? "default") as NoteColor;
     labelList.value = n ? [...n.labels] : [];
-    baseline.value = { body: n?.body ?? "", color: (n?.color ?? "default") as NoteColor };
+    baseline.value = { body: n?.body ?? "" };
   },
 );
 
 // ---- persistence ----
 async function createFromFields(): Promise<void> {
-  const created = await notes.create({ body: body.value, color: color.value });
+  const created = await notes.create({ body: body.value });
   noteId.value = created.id;
-  baseline.value = { body: created.body, color: created.color as NoteColor };
+  baseline.value = { body: created.body };
 }
 
 // Ensure a persisted note exists (for rich actions mid-compose). Returns its id, or
@@ -161,12 +154,12 @@ async function flush(): Promise<void> {
   }
   const b = baseline.value;
   const nextBody = body.value;
-  const changed = nextBody !== b.body || color.value !== b.color;
+  const changed = nextBody !== b.body;
   if (!changed) return;
   saving.value = true;
   try {
-    await notes.saveEdit(noteId.value as string, { body: nextBody, color: color.value });
-    baseline.value = { body: nextBody, color: color.value };
+    await notes.saveEdit(noteId.value as string, { body: nextBody });
+    baseline.value = { body: nextBody };
   } finally {
     saving.value = false;
   }
@@ -175,9 +168,8 @@ async function flush(): Promise<void> {
 function resetCompose(): void {
   noteId.value = null;
   setBody("");
-  color.value = "default";
   labelList.value = [];
-  baseline.value = { body: "", color: "default" };
+  baseline.value = { body: "" };
   uploadError.value = "";
 }
 
@@ -468,8 +460,7 @@ async function restoreRevisionAt(revId: string) {
   if (!id) return;
   const updated = await notes.restoreRevision(id, revId);
   setBody(updated.body);
-  color.value = updated.color;
-  baseline.value = { body: updated.body, color: updated.color };
+  baseline.value = { body: updated.body };
   void loadRevisions(); // the pre-restore state became a new revision
 }
 function revLabel(iso: string | null): string {
@@ -713,8 +704,10 @@ function revPreview(rev: NoteRevision): string {
         </div>
       </div>
 
-      <div class="flex items-center justify-between gap-2 border-t border-neutral-100 px-3 py-2 dark:border-neutral-800">
-        <ColorPicker v-model="color" />
+      <!-- `justify-end`, not `justify-between`: the colour picker sat on the left of
+           this row until M315 and the row was balanced around it. With one child left,
+           `between` would push the actions to the far left of a full-width bar. -->
+      <div class="flex items-center justify-end gap-2 border-t border-neutral-100 px-3 py-2 dark:border-neutral-800">
         <div class="flex items-center gap-0.5">
           <button
             v-if="richEnabled && !liveNote.trashed"