labels: per-label color

Give labels a color (migration 0011 adds labels.color, server_default
'default' so existing labels keep the neutral chip). The PATCH endpoint now
updates name and/or color; note serialization carries each label's color.
Frontend: a swatch picker per label in the Edit-labels modal, colored chips
on cards + in the editor (LABEL_CHIP_CLASSES), and a color dot on each
sidebar label. Reuses the note color vocabulary. (Graph node coloring rides
this in the graph-liveliness task.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

src/thoughtsync/labels.py

@@ -12,8 +12,15 @@ from .models.label import Label
 bp = Blueprint("labels", __name__, url_prefix="/api/labels")
 
 
+LABEL_COLORS = {"default", "red", "orange", "yellow", "green", "teal", "blue", "purple", "pink", "gray"}
+
+
+def _normalize_label_color(color: object) -> str:
+    return color if color in LABEL_COLORS else "default"
+
+
 def _serialize_label(label: Label) -> dict:
-    return {"id": str(label.id), "name": label.name}
+    return {"id": str(label.id), "name": label.name, "color": label.color}
 
 
 async def _get_owned_label(db, label_id: str) -> Label | None:
@@ -44,7 +51,7 @@ async def create_label():
         existing = await db.scalar(select(Label).where(Label.owner_id == g.user_id, Label.name == name))
         if existing is not None:
             return jsonify(_serialize_label(existing)), 200
-        label = Label(owner_id=g.user_id, name=name)
+        label = Label(owner_id=g.user_id, name=name, color=_normalize_label_color(data.get("color")))
         db.add(label)
         await db.commit()
         await db.refresh(label)
@@ -53,21 +60,28 @@ async def create_label():
 
 @bp.patch("/<label_id>")
 @login_required
-async def rename_label(label_id: str):
+async def update_label(label_id: str):
     data = await request.get_json(silent=True) or {}
-    name = (data.get("name") or "").strip()
-    if not name:
+    has_name = "name" in data
+    has_color = "color" in data
+    if not has_name and not has_color:
+        return jsonify({"error": "nothing to update"}), 400
+    name = (data.get("name") or "").strip() if has_name else None
+    if has_name and not name:
         return jsonify({"error": "label name is required"}), 400
     async with session_scope() as db:
         label = await _get_owned_label(db, label_id)
         if label is None:
             return jsonify({"error": "not found"}), 404
-        clash = await db.scalar(
-            select(Label).where(Label.owner_id == g.user_id, Label.name == name, Label.id != label.id)
-        )
-        if clash is not None:
-            return jsonify({"error": "a label with that name already exists"}), 409
-        label.name = name
+        if has_name:
+            clash = await db.scalar(
+                select(Label).where(Label.owner_id == g.user_id, Label.name == name, Label.id != label.id)
+            )
+            if clash is not None:
+                return jsonify({"error": "a label with that name already exists"}), 409
+            label.name = name
+        if has_color:
+            label.color = _normalize_label_color(data.get("color"))
         await db.commit()
         await db.refresh(label)
         return jsonify(_serialize_label(label))