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/agents/timeline_agent.py

@@ -1,30 +1,13 @@
-"""Timeline agent — project milestone management (list, create, update, delete)."""
+"""Timeline agent — tool definitions for project milestone CRUD."""
 
 from __future__ import annotations
 
-import json
 from typing import Any
 
-from langchain_core.messages import HumanMessage, SystemMessage
 from langchain_core.tools import tool
 
-from app.core.agent_registry import ChatAgent, registry
-from app.core.llm import get_llm
 from app.core.ws_context import execute_on_client
 
-_SYSTEM_PROMPT = (
-    "You are a project timeline assistant. Timelines are milestone dates that\n"
-    "track progress on a project — they are not calendar events.\n\n"
-    "Rules:\n"
-    "  - project_id is REQUIRED for every create; confirm with the user if unknown\n"
-    "  - date is a Unix timestamp in milliseconds; convert human-readable dates\n"
-    "  - is_ai_suggested: 1 when proactively proposing a timeline, 0 otherwise\n"
-    "  - is_approved: 0 until the user explicitly confirms; then 1\n"
-    "  - For update_timeline, use -1 for integer fields you do not want to change\n"
-    "  - Listing without a project_id returns all timelines across projects\n"
-    "  - Always echo the title and formatted date in your confirmation."
-)
-
 
 @tool
 async def list_timelines(project_id: str = "") -> str:
@@ -106,23 +89,4 @@ async def delete_timeline(timeline_id: str) -> str:
     return f"Timeline {timeline_id} deleted."
 
 
-@registry.register
-class TimelineAgent(ChatAgent):
-    def get_name(self) -> str:
-        return "timeline_agent"
 
-    def get_description(self) -> str:
-        return "Manages project timelines (milestones): list, create, update, delete"
-
-    def get_tools(self) -> list[Any]:
-        return [list_timelines, create_timeline, update_timeline, delete_timeline]
-
-    async def handle(self, query: str, context: dict[str, Any]) -> str:
-        llm = get_llm()
-        messages = [
-            SystemMessage(content=_SYSTEM_PROMPT),
-            HumanMessage(
-                content=f"User query: {query}\nContext: {json.dumps(context)[:1000]}"
-            ),
-        ]
-        return await self._tool_loop(llm, messages, self.get_tools())