feat: brain colored folders/tags — color + icon fields, mobile pills

Backend:
- Added color (hex) and icon (lucide name) columns to folders and tags
- Default folders seeded with colors: Home=green, Work=indigo, Travel=blue, etc.
- API returns color/icon in sidebar and CRUD responses
- Create/update endpoints accept color and icon

Frontend:
- Mobile: horizontal scrollable pill tabs with colored dots
- Desktop sidebar: colored dots next to folder names
- Active pill gets tinted border matching folder color

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/brain/app/models/taxonomy.py

@@ -29,6 +29,8 @@ class Folder(Base):
     user_id = Column(String(64), nullable=False, index=True)
     name = Column(String(128), nullable=False)
     slug = Column(String(128), nullable=False)
+    color = Column(String(7), nullable=True)        # hex like #4F46E5
+    icon = Column(String(32), nullable=True)         # lucide icon name like "home"
     is_active = Column(Boolean, default=True, nullable=False)
     sort_order = Column(Integer, default=0, nullable=False)
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
@@ -46,6 +48,8 @@ class Tag(Base):
     user_id = Column(String(64), nullable=False, index=True)
     name = Column(String(128), nullable=False)
     slug = Column(String(128), nullable=False)
+    color = Column(String(7), nullable=True)
+    icon = Column(String(32), nullable=True)
     is_active = Column(Boolean, default=True, nullable=False)
     sort_order = Column(Integer, default=0, nullable=False)
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
@@ -64,8 +68,16 @@ class ItemTag(Base):
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
 
 
-# Default folders to seed for new users
-DEFAULT_FOLDERS = ["Home", "Family", "Work", "Travel", "Knowledge", "Faith", "Projects"]
+# Default folders with colors and icons
+DEFAULT_FOLDERS = [
+    {"name": "Home",      "color": "#059669", "icon": "home"},
+    {"name": "Family",    "color": "#D97706", "icon": "heart"},
+    {"name": "Work",      "color": "#4338CA", "icon": "briefcase"},
+    {"name": "Travel",    "color": "#0EA5E9", "icon": "plane"},
+    {"name": "Knowledge", "color": "#8B5CF6", "icon": "book-open"},
+    {"name": "Faith",     "color": "#10B981", "icon": "moon"},
+    {"name": "Projects",  "color": "#F43F5E", "icon": "folder"},
+]
 
 # Default tags to seed for new users
 DEFAULT_TAGS = [
@@ -87,8 +99,9 @@ async def ensure_user_taxonomy(db, user_id: str):
     )).scalar() or 0
 
     if folder_count == 0:
-        for i, name in enumerate(DEFAULT_FOLDERS):
-            db.add(Folder(id=new_id(), user_id=user_id, name=name, slug=slugify(name), sort_order=i))
+        for i, f in enumerate(DEFAULT_FOLDERS):
+            db.add(Folder(id=new_id(), user_id=user_id, name=f["name"], slug=slugify(f["name"]),
+                          color=f.get("color"), icon=f.get("icon"), sort_order=i))
         await db.flush()
 
     tag_count = (await db.execute(