feat: major platform expansion — Brain service, RSS reader, iOS app, AI assistants, Firefox extension

Brain Service:
- Playwright stealth crawler replacing browserless (og:image, Readability, Reddit JSON API)
- AI classification with tag definitions and folder assignment
- YouTube video download via yt-dlp
- Karakeep migration complete (96 items)
- Taxonomy management (folders with icons/colors, tags)
- Discovery shuffle, sort options, search (Meilisearch + pgvector)
- Item tag/folder editing, card color accents

RSS Reader Service:
- Custom FastAPI reader replacing Miniflux
- Feed management (add/delete/refresh), category support
- Full article extraction via Readability
- Background content fetching for new entries
- Mark all read with confirmation
- Infinite scroll, retention cleanup (30/60 day)
- 17 feeds migrated from Miniflux

iOS App (SwiftUI):
- Native iOS 17+ app with @Observable architecture
- Cookie-based auth, configurable gateway URL
- Dashboard with custom background photo + frosted glass widgets
- Full fitness module (today/templates/goals/food library)
- AI assistant chat (fitness + brain, raw JSON state management)
- 120fps ProMotion support

AI Assistants (Gateway):
- Unified dispatcher with fitness/brain domain detection
- Fitness: natural language food logging, photo analysis, multi-item splitting
- Brain: save/append/update/delete notes, search & answer, undo support
- Madiha user gets fitness-only (brain disabled)

Firefox Extension:
- One-click save to Brain from any page
- Login with platform credentials
- Right-click context menu (save page/link/image)
- Notes field for URL saves
- Signed and published on AMO

Other:
- Reader bookmark button routes to Brain (was Karakeep)
- Fitness food library with "Add" button + add-to-meal popup
- Kindle send file size check (25MB SMTP2GO limit)
- Atelier UI as default (useAtelierShell=true)
- Mobile upload box in nav drawer

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

services/brain/app/models/item.py

@@ -45,6 +45,12 @@ class Item(Base):
 
     # Relationships
     assets = relationship("ItemAsset", back_populates="item", cascade="all, delete-orphan")
+    additions = relationship(
+        "ItemAddition",
+        back_populates="item",
+        cascade="all, delete-orphan",
+        order_by="ItemAddition.created_at",
+    )
 
     __table_args__ = (
         Index("ix_items_user_status", "user_id", "processing_status"),
@@ -79,3 +85,19 @@ class AppLink(Base):
     app = Column(String(64), nullable=False)       # trips|tasks|fitness|inventory
     app_entity_id = Column(String(128), nullable=False)
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+
+
+class ItemAddition(Base):
+    __tablename__ = "item_additions"
+
+    id = Column(UUID(as_uuid=False), primary_key=True, default=new_id)
+    item_id = Column(UUID(as_uuid=False), ForeignKey("items.id", ondelete="CASCADE"), nullable=False, index=True)
+    user_id = Column(String(64), nullable=False, index=True)
+    source = Column(String(32), nullable=False, default="assistant")  # assistant|manual
+    kind = Column(String(32), nullable=False, default="append")  # append
+    content = Column(Text, nullable=False)
+    metadata_json = Column(JSONB, nullable=True, default=dict)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)
+
+    item = relationship("Item", back_populates="additions")