Get STPT MCP service status

Added value: +{
+  "enum": [
+    "fresh",
+    "stale",
+    "unverified"
+  ],
+  "title": "Freshness",
+  "type": "string"
+}

Added value: +{
+  "additionalProperties": false,
+  "properties": {
+    "assessed_at": {
+      "description": "When that fetch was assessed, in UTC.",
+      "format": "date-time",
+      "title": "Assessed At",
+      "type": "string"
+    },
+    "clock_unchanged_seconds": {
+      "description": "How long that stop's feed clock has stood still while real time advanced.",
+      "minimum": 0,
+      "title": "Clock Unchanged Seconds",
+      "type": "number"
+    },
+    "freshness": {
+      "$ref": "#/$defs/Freshness"
+    },
+    "recent_stops": {
+      "additionalProperties": {
+        "type": "integer"
+      },
+      "description": "Freshness of every stop fetched in the last 15 minutes, counted.",
+      "propertyNames": {
+        "$ref": "#/$defs/Freshness"
+      },
+      "title": "Recent Stops",
+      "type": "object"
+    },
+    "skew_seconds": {
+      "anyOf": [
+        {
+          "type": "number"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "default": null,
+      "description": "The feed's implied clock minus the real clock, in seconds. Positive means the feed runs ahead. Null when the feed carried no clock reference.",
+      "title": "Skew Seconds"
+    },
+    "stop_id": {
+      "description": "Stop of the most recent live arrivals fetch.",
+      "title": "Stop Id",
+      "type": "string"
+    }
+  },
+  "required": [
+    "stop_id",
+    "assessed_at",
+    "freshness",
+    "clock_unchanged_seconds"
+  ],
+  "title": "LiveFeedStatus",
+  "type": "object"
+}

Previous value: -"Age of the source/cache entry when returned."New value: +"Age of the upstream observation when returned, in seconds. Null when the age cannot be measured."

Added value: +{
+  "$ref": "#/$defs/Freshness",
+  "default": "unverified",
+  "description": "fresh: an upstream observation time was checked against this server's clock and is within tolerance. stale: the check failed (old, clock-skewed, or frozen data) or a cache entry past its TTL is served. unverified: the data carries no upstream clock reference (schedules, the network snapshot, alerts), so it cannot be confirmed as current."
+}

Previous value: -"True when the stale cache policy supplied the data."New value: +"True when stale data is being returned, whether from cache or upstream."

Previous value: -"Upstream observation timestamp. Live arrivals expose no timestamp, so this is the fetch time; schedules describe future service and leave it null; vehicles use their upstream timestamp."New value: +"Upstream observation timestamp in UTC. Live arrivals derive it from the feed's own display times and remaining minutes; it is null when the feed carries no clock reference or is rejected as stale. Schedules describe future service and leave it null; vehicles use their upstream timestamp."

Added value: +{
+  "anyOf": [
+    {
+      "$ref": "#/$defs/LiveFeedStatus"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "default": null,
+  "description": "Freshness of the live arrivals feed. Null until a stop has been fetched."
+}