feat: schedule type system for work/entertainment periods

- New model: ScheduleType (name, work_from/to, entertainment_from/to)
- Agent.schedule_type_id FK to schedule_types
- CRUD API: GET/POST/PATCH/DELETE /schedule-types/
- Agent assignment: PUT /schedule-types/agent/{agent_id}/assign
- Agent self-query: GET /schedule-types/agent/me
- Permissions: schedule_type.read, schedule_type.manage
- Migration: adds schedule_type_id column to agents table

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/models/agent.py

@@ -131,6 +131,15 @@ class Agent(Base):
         comment="rate_limit | billing — why the agent is exhausted",
     )
 
+    # -- schedule type ------------------------------------------------------
+
+    schedule_type_id = Column(
+        Integer,
+        ForeignKey("schedule_types.id"),
+        nullable=True,
+        comment="FK to schedule_types — defines work/entertainment periods",
+    )
+
     # -- timestamps ---------------------------------------------------------
 
     created_at = Column(DateTime(timezone=True), server_default=func.now())
@@ -138,3 +147,4 @@ class Agent(Base):
     # -- relationships ------------------------------------------------------
 
     user = relationship("User", back_populates="agent", uselist=False)
+    schedule_type = relationship("ScheduleType", lazy="joined")