feat: add configuration management API endpoints

- api_get_config.py: retrieve current DECNET config (admin only)
- api_update_config.py: modify deployment settings (admin only)
- api_manage_users.py: user/role management (admin only)
- api_reinit.py: reinitialize database schema (admin only)
- Integrated with centralized RBAC per memory: server-side UI gating

decnet/web/router/config/api_update_config.py

@@ -0,0 +1,43 @@
+from fastapi import APIRouter, Depends
+
+from decnet.web.dependencies import require_admin, repo
+from decnet.web.db.models import DeploymentLimitRequest, GlobalMutationIntervalRequest
+
+router = APIRouter()
+
+
+@router.put(
+    "/config/deployment-limit",
+    tags=["Configuration"],
+    responses={
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Admin access required"},
+        422: {"description": "Validation error"},
+    },
+)
+async def api_update_deployment_limit(
+    req: DeploymentLimitRequest,
+    admin: dict = Depends(require_admin),
+) -> dict[str, str]:
+    await repo.set_state("config_limits", {"deployment_limit": req.deployment_limit})
+    return {"message": "Deployment limit updated"}
+
+
+@router.put(
+    "/config/global-mutation-interval",
+    tags=["Configuration"],
+    responses={
+        401: {"description": "Could not validate credentials"},
+        403: {"description": "Admin access required"},
+        422: {"description": "Validation error"},
+    },
+)
+async def api_update_global_mutation_interval(
+    req: GlobalMutationIntervalRequest,
+    admin: dict = Depends(require_admin),
+) -> dict[str, str]:
+    await repo.set_state(
+        "config_globals",
+        {"global_mutation_interval": req.global_mutation_interval},
+    )
+    return {"message": "Global mutation interval updated"}