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/models/coord_session_lock.py

@@ -0,0 +1,64 @@
+"""Coordination session lock model."""
+
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import DateTime, Index, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.sql import func
+
+from .base import Base, TimestampMixin, UUIDMixin
+
+
+class CoordSessionLock(Base, UUIDMixin, TimestampMixin):
+    """An exclusive lock held by a session on a resource path."""
+
+    __tablename__ = "coord_session_locks"
+
+    project_key: Mapped[str] = mapped_column(
+        String(200),
+        nullable=False,
+        doc="Project namespace this lock applies to"
+    )
+
+    session_id: Mapped[str] = mapped_column(
+        String(200),
+        nullable=False,
+        doc="Session holding the lock, e.g. 'DESKTOP-0O8A1RL/Claude'"
+    )
+
+    resource: Mapped[str] = mapped_column(
+        String(500),
+        nullable=False,
+        doc="Resource path being locked, e.g. 'server/src/', 'migrations/'"
+    )
+
+    description: Mapped[Optional[str]] = mapped_column(
+        Text,
+        doc="Why this lock was acquired"
+    )
+
+    acquired_at: Mapped[datetime] = mapped_column(
+        DateTime,
+        nullable=False,
+        server_default=func.now(),
+        doc="When the lock was claimed"
+    )
+
+    expires_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime,
+        doc="NULL means no expiry; otherwise the lock expires at this time"
+    )
+
+    released_at: Mapped[Optional[datetime]] = mapped_column(
+        DateTime,
+        doc="NULL means still held; set when lock is explicitly released"
+    )
+
+    __table_args__ = (
+        Index("idx_coord_locks_project_resource", "project_key", "resource"),
+        Index("idx_coord_locks_session", "session_id"),
+    )
+
+    def __repr__(self) -> str:
+        return f"<CoordSessionLock(project_key='{self.project_key}', resource='{self.resource}', session_id='{self.session_id}')>"