BE-CAL-004: implement MinimumWorkload storage

- New model: minimum_workloads table with JSON config column (per-user)
- Schemas: MinimumWorkloadConfig, MinimumWorkloadUpdate, MinimumWorkloadResponse
- Service: CRUD operations + check_workload_warnings() entry point for BE-CAL-007
- API: GET/PUT/PATCH /calendar/workload-config (self + admin routes)
- Migration: auto-create minimum_workloads table on startup
- Registered calendar router in main.py

app/main.py

@@ -62,6 +62,7 @@ from app.api.routers.proposes import router as proposes_router  # legacy compat
 from app.api.routers.milestone_actions import router as milestone_actions_router
 from app.api.routers.meetings import router as meetings_router
 from app.api.routers.essentials import router as essentials_router
+from app.api.routers.calendar import router as calendar_router
 
 app.include_router(auth_router)
 app.include_router(tasks_router)
@@ -78,6 +79,7 @@ app.include_router(proposes_router)  # legacy compat
 app.include_router(milestone_actions_router)
 app.include_router(meetings_router)
 app.include_router(essentials_router)
+app.include_router(calendar_router)
 
 
 # Auto schema migration for lightweight deployments
@@ -303,6 +305,21 @@ def _migrate_schema():
                 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
             """))
 
+        # --- minimum_workloads table (BE-CAL-004) ---
+        if not _has_table(db, "minimum_workloads"):
+            db.execute(text("""
+                CREATE TABLE minimum_workloads (
+                    id INTEGER NOT NULL AUTO_INCREMENT,
+                    user_id INTEGER NOT NULL,
+                    config JSON NOT NULL,
+                    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+                    updated_at DATETIME NULL ON UPDATE CURRENT_TIMESTAMP,
+                    PRIMARY KEY (id),
+                    UNIQUE INDEX idx_minimum_workloads_user_id (user_id),
+                    CONSTRAINT fk_minimum_workloads_user_id FOREIGN KEY (user_id) REFERENCES users(id)
+                ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
+            """))
+
         db.commit()
     except Exception as e:
         db.rollback()
@@ -337,7 +354,7 @@ def _sync_default_user_roles(db):
 @app.on_event("startup")
 def startup():
     from app.core.config import Base, engine, SessionLocal
-    from app.models import models, webhook, apikey, activity, milestone, notification, worklog, monitor, role_permission, task, support, meeting, proposal, propose, essential, agent, calendar
+    from app.models import models, webhook, apikey, activity, milestone, notification, worklog, monitor, role_permission, task, support, meeting, proposal, propose, essential, agent, calendar, minimum_workload
     Base.metadata.create_all(bind=engine)
     _migrate_schema()