Add shared notes with tabbed pages editable by user and AI

Adds a note_pages table backing a tabbed notes panel where the user and
the model can both read and write. Only page titles (plus a short
preview) are injected into the system prompt on every turn; full page
content is kept out of context and fetched on demand via a read_note
tool, with write_note letting the model append to, replace, or create a
page.

Generalizes llm.resolve_web_search into resolve_tool_calls so the
tool-calling loop handles web_search and the new note tools through one
path. The chat stream emits a notes_updated SSE event when the model
edits a note so the frontend panel can refresh; local edits are tracked
as dirty and never clobbered by that refresh.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/app/main.py

@@ -5,7 +5,7 @@ from fastapi import Depends, FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.api import auth as auth_api
-from app.api import chat, logs, memory, system
+from app.api import chat, logs, memory, notes, system
 from app.api import models as models_api
 from app.api import settings as settings_api
 from app.core import settings_store
@@ -93,6 +93,7 @@ app.add_middleware(
 app.include_router(auth_api.router)
 app.include_router(chat.router, dependencies=[Depends(require_site_session)])
 app.include_router(memory.router, dependencies=[Depends(require_site_session)])
+app.include_router(notes.router, dependencies=[Depends(require_site_session)])
 app.include_router(logs.router, dependencies=[Depends(require_site_session)])
 app.include_router(system.router, dependencies=[Depends(require_site_session)])
 app.include_router(settings_api.router, dependencies=[Depends(require_site_session)])