feat: agent coordination system (workflows, locks, components, messages)

Adds /api/coord/* endpoints for real-time cross-session coordination:
- coord_workflows: named units of work per project
- coord_work_items: tasks within workflows with dependency chains
- coord_session_locks: exclusive resource locks with auto-expiry (TTL)
- coord_component_states: live component state per project (upsert)
- coord_messages: cross-session messaging and broadcasts
- /api/coord/status: cross-project snapshot endpoint

Replaces PROJECT_STATE.md as the coordination layer for Claude sessions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/schemas/coord_work_item.py

@@ -0,0 +1,53 @@
+"""Pydantic schemas for CoordWorkItem."""
+
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+
+from pydantic import BaseModel, Field
+
+
+class CoordWorkItemCreate(BaseModel):
+    """Input schema for creating a work item."""
+
+    workflow_id: str = Field(..., description="Parent workflow UUID", max_length=36)
+    project_key: str = Field(..., description="Project namespace slug", max_length=200)
+    title: str = Field(..., description="Short title", max_length=500)
+    description: Optional[str] = Field(None, description="Full description, markdown ok")
+    status: str = Field("pending", description="Status: pending, in_progress, blocked, completed, cancelled")
+    priority: int = Field(0, description="Higher value = more urgent")
+    assigned_session: Optional[str] = Field(None, max_length=200)
+    depends_on_id: Optional[str] = Field(None, description="Blocking predecessor item UUID", max_length=36)
+
+
+class CoordWorkItemUpdate(BaseModel):
+    """Input schema for updating a work item. All fields optional."""
+
+    title: Optional[str] = Field(None, max_length=500)
+    description: Optional[str] = None
+    status: Optional[str] = Field(None, description="Status: pending, in_progress, blocked, completed, cancelled")
+    priority: Optional[int] = None
+    assigned_session: Optional[str] = Field(None, max_length=200)
+    depends_on_id: Optional[str] = Field(None, max_length=36)
+    started_at: Optional[datetime] = None
+    completed_at: Optional[datetime] = None
+
+
+class CoordWorkItemResponse(BaseModel):
+    """Output schema for a work item."""
+
+    id: UUID
+    workflow_id: str
+    project_key: str
+    title: str
+    description: Optional[str]
+    status: str
+    priority: int
+    assigned_session: Optional[str]
+    depends_on_id: Optional[str]
+    started_at: Optional[datetime]
+    completed_at: Optional[datetime]
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = {"from_attributes": True}