refactor: replace orchestrator with LangGraph deep-agent supervisors

- Add app/core/deep_agent.py with Home and Floating supervisor graphs
  using LangGraph create_react_agent (hierarchical pattern)
- Strip ChatAgent classes from all 4 agent files, keep @tool functions
- Rewrite output_formatter.py for event-based (token/tool_end/mutations) stream
- Update device_ws.py to use run_home_stream/run_floating_stream
- Rewrite chat.py REST route to use run_home
- Add update_core_memory tool to both supervisors
- Add langgraph>=0.3.0 to requirements.txt
- Remove orchestrator.py, execution_plan.py, agent_registry.py, plans.py
- Remove PlanAction, PlanStep, ExecutionPlan, execution_mode from schemas
- Update all affected tests to match new API
- Remove 6 deprecated test files for deleted modules
- Clean up stale docstrings referencing removed orchestrator

app/main.py

@@ -18,10 +18,7 @@ from app.config.settings import settings
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
-    # Startup: initialise DB connection pool and agent registry
-    from app.core.agent_registry import registry  # noqa: F401 — triggers module load
-    import app.agents  # noqa: F401 — triggers @registry.register decorators
-
+    # Startup: initialise DB connection pool
     yield
 
     # Shutdown: dispose SQLAlchemy connection pool
@@ -51,11 +48,10 @@ def create_app() -> FastAPI:
     app.add_middleware(SanitizerMiddleware)
     app.add_middleware(TierRateLimitMiddleware)
 
-    from app.api.routes import agent_setup, agents, auth, backup, billing, chat, device_ws, plans, plugins, storage, vectors
+    from app.api.routes import agent_setup, agents, auth, backup, billing, chat, device_ws, plugins, storage, vectors
 
     app.include_router(auth.router,       prefix="/api/v1")
     app.include_router(chat.router,       prefix="/api/v1")
-    app.include_router(plans.router,      prefix="/api/v1")
     app.include_router(storage.router,    prefix="/api/v1")
     app.include_router(vectors.router,    prefix="/api/v1")
     app.include_router(backup.router,     prefix="/api/v1")