feat: crash recovery, service_failed monitoring, broker health fields, command expiry sweep

- Add GET /api/clients/crashed endpoint (process_status=crashed or stale heartbeat)
- Add restart_app command action with same lifecycle + lockout as reboot_host
- Scheduler: crash auto-recovery loop (CRASH_RECOVERY_ENABLED flag, lockout, MQTT publish)
- Scheduler: unconditional command expiry sweep per poll cycle (sweep_expired_commands)
- Listener: subscribe to infoscreen/+/service_failed; persist service_failed_at + unit
- Listener: extract broker_connection block from health payload; persist reconnect_count + last_disconnect_at
- DB migration b1c2d3e4f5a6: service_failed_at, service_failed_unit, mqtt_reconnect_count, mqtt_last_disconnect_at on clients
- Add GET /api/clients/service_failed and POST /api/clients/<uuid>/clear_service_failed
- Monitoring overview API: include mqtt_reconnect_count + mqtt_last_disconnect_at per client
- Frontend: orange service-failed alert panel (hidden when empty, auto-refresh, quittieren action)
- Frontend: MQTT reconnect count + last disconnect in client detail panel
- MQTT auth hardening: listener/scheduler/server use env credentials; broker enforces allow_anonymous false
- Client command lifecycle foundation: ClientCommand model, reboot_host/shutdown_host, full ACK lifecycle
- Docs: TECH-CHANGELOG, DEV-CHANGELOG, MQTT_EVENT_PAYLOAD_GUIDE, copilot-instructions updated
- Add implementation-plans/, RESTART_VALIDATION_CHECKLIST.md, TODO.md

implementation-plans/reboot-command-payload-schemas.json

@@ -0,0 +1,149 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://infoscreen.local/schemas/reboot-command-payload-schemas.json",
+  "title": "Infoscreen Reboot Command Payload Schemas",
+  "description": "Frozen v1 schemas for per-client command and command acknowledgement payloads.",
+  "$defs": {
+    "commandPayloadV1": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "schema_version",
+        "command_id",
+        "client_uuid",
+        "action",
+        "issued_at",
+        "expires_at",
+        "requested_by",
+        "reason"
+      ],
+      "properties": {
+        "schema_version": {
+          "type": "string",
+          "const": "1.0"
+        },
+        "command_id": {
+          "type": "string",
+          "format": "uuid"
+        },
+        "client_uuid": {
+          "type": "string",
+          "format": "uuid"
+        },
+        "action": {
+          "type": "string",
+          "enum": [
+            "reboot_host",
+            "shutdown_host"
+          ]
+        },
+        "issued_at": {
+          "type": "string",
+          "format": "date-time"
+        },
+        "expires_at": {
+          "type": "string",
+          "format": "date-time"
+        },
+        "requested_by": {
+          "type": [
+            "integer",
+            "null"
+          ],
+          "minimum": 1
+        },
+        "reason": {
+          "type": [
+            "string",
+            "null"
+          ],
+          "maxLength": 2000
+        }
+      }
+    },
+    "commandAckPayloadV1": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": [
+        "command_id",
+        "status",
+        "error_code",
+        "error_message"
+      ],
+      "properties": {
+        "command_id": {
+          "type": "string",
+          "format": "uuid"
+        },
+        "status": {
+          "type": "string",
+          "enum": [
+            "accepted",
+            "execution_started",
+            "completed",
+            "failed"
+          ]
+        },
+        "error_code": {
+          "type": [
+            "string",
+            "null"
+          ],
+          "maxLength": 128
+        },
+        "error_message": {
+          "type": [
+            "string",
+            "null"
+          ],
+          "maxLength": 4000
+        }
+      },
+      "allOf": [
+        {
+          "if": {
+            "properties": {
+              "status": {
+                "const": "failed"
+              }
+            }
+          },
+          "then": {
+            "properties": {
+              "error_code": {
+                "type": "string",
+                "minLength": 1
+              },
+              "error_message": {
+                "type": "string",
+                "minLength": 1
+              }
+            }
+          }
+        }
+      ]
+    }
+  },
+  "examples": [
+    {
+      "commandPayloadV1": {
+        "schema_version": "1.0",
+        "command_id": "5d1f8b4b-7e85-44fb-8f38-3f5d5da5e2e4",
+        "client_uuid": "9b8d1856-ff34-4864-a726-12de072d0f77",
+        "action": "reboot_host",
+        "issued_at": "2026-04-03T12:48:10Z",
+        "expires_at": "2026-04-03T12:52:10Z",
+        "requested_by": 1,
+        "reason": "operator_request"
+      }
+    },
+    {
+      "commandAckPayloadV1": {
+        "command_id": "5d1f8b4b-7e85-44fb-8f38-3f5d5da5e2e4",
+        "status": "execution_started",
+        "error_code": null,
+        "error_message": null
+      }
+    }
+  ]
+}