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>

android/ffi/src/lib.rs

@@ -617,7 +617,6 @@ mod tests {
     fn draft(body: &str) -> NoteDraft {
         NoteDraft {
             body: body.to_string(),
-            color: "default".to_string(),
             items: None,
         }
     }
@@ -671,8 +670,7 @@ mod tests {
         let created = app
             .create_note(NoteDraft {
                 body: String::new(),
-                color: "default".to_string(),
-                items: Some(vec!["milk".to_string(), "eggs".to_string()]),
+                    items: Some(vec!["milk".to_string(), "eggs".to_string()]),
             })
             .expect("create should succeed");
         assert_eq!(created.display_title, "milk");
@@ -707,8 +705,7 @@ mod tests {
         let note = app
             .create_note(NoteDraft {
                 body: "Packing".to_string(),
-                color: "default".to_string(),
-                items: Some(vec!["socks".to_string()]),
+                    items: Some(vec!["socks".to_string()]),
             })
             .expect("create");
         assert_eq!(note.items.len(), 1);

android/ffi/src/models.rs

@@ -33,7 +33,6 @@ pub struct Note {
     /// Always present. Derived by the core, never stored.
     pub display_title: String,
     pub body: String,
-    pub color: String,
     pub position: i64,
     pub pinned: bool,
     pub archived: bool,
@@ -187,7 +186,6 @@ impl From<core_models::Note> for Note {
             id,
             display_title,
             body,
-            color,
             position,
             pinned,
             archived,
@@ -206,7 +204,6 @@ impl From<core_models::Note> for Note {
             id,
             display_title,
             body,
-            color,
             position,
             pinned,
             archived,
@@ -344,7 +341,6 @@ pub struct NoteQuery {
 #[derive(Debug, Clone, uniffi::Record)]
 pub struct NoteFacets {
     pub q: Option<String>,
-    pub color: Option<String>,
     pub label: Option<Vec<String>>,
     pub has_reminder: Option<bool>,
     pub has_attachment: Option<bool>,
@@ -373,7 +369,6 @@ impl From<NoteFacets> for core_models::Facets {
     fn from(value: NoteFacets) -> Self {
         let NoteFacets {
             q,
-            color,
             label,
             has_reminder,
             has_attachment,
@@ -382,7 +377,6 @@ impl From<NoteFacets> for core_models::Facets {
         } = value;
         core_models::Facets {
             q,
-            color,
             label,
             has_reminder,
             has_attachment,
@@ -396,8 +390,6 @@ impl From<NoteFacets> for core_models::Facets {
 #[derive(Debug, Clone, uniffi::Record)]
 pub struct NoteDraft {
     pub body: String,
-    /// "default" unless the user picked a colour.
-    pub color: String,
     /// Checklist lines. A note can carry both a body and items (M13 step 2), so this
     /// is not an alternative to `body` — it is an addition to it.
     pub items: Option<Vec<String>>,
@@ -405,8 +397,8 @@ pub struct NoteDraft {
 
 impl From<NoteDraft> for core_models::NoteCreateInput {
     fn from(value: NoteDraft) -> Self {
-        let NoteDraft { body, color, items } = value;
-        core_models::NoteCreateInput { body, color, items }
+        let NoteDraft { body, items } = value;
+        core_models::NoteCreateInput { body, items }
     }
 }
 
@@ -421,7 +413,6 @@ impl From<NoteDraft> for core_models::NoteCreateInput {
 #[derive(Debug, Clone, uniffi::Enum)]
 pub enum NoteEdit {
     Body { value: String },
-    Color { value: String },
     Pinned { value: bool },
     Archived { value: bool },
     RemindAt { value: String },
@@ -441,7 +432,6 @@ impl NoteEdit {
         use serde_json::Value;
         match self {
             NoteEdit::Body { value } => ("body", Value::String(value)),
-            NoteEdit::Color { value } => ("color", Value::String(value)),
             NoteEdit::Pinned { value } => ("pinned", Value::Bool(value)),
             NoteEdit::Archived { value } => ("archived", Value::Bool(value)),
             NoteEdit::RemindAt { value } => ("remind_at", Value::String(value)),