Add camera snapshot messages and flag for P1/A1 cameras

camera_snapshot_request (cloud to gateway) and camera_snapshot (gateway
to cloud) carry one JPEG frame at a time; telemetry gains camera_snapshot
and the app view gains cameraSnapshot.

schemas/continuum/v1/edge/client_message.schema.json

@@ -183,6 +183,18 @@
         "message"
       ]
     },
+    {
+      "type": "object",
+      "title": "CameraSnapshot",
+      "description": "The answer to a CameraSnapshotRequest: one JPEG frame (base64), or the reason there is none.",
+      "properties": {
+        "type": { "const": "camera_snapshot" },
+        "request_id": { "type": "string" },
+        "jpeg_base64": { "type": "string" },
+        "error": { "type": "string", "description": "Set instead of jpeg_base64 when no frame could be read." }
+      },
+      "required": ["type", "request_id"]
+    },
     {
       "type": "object",
       "title": "DiscoveredPrinters",

schemas/continuum/v1/edge/printer_telemetry.schema.json

@@ -108,7 +108,11 @@
     },
     "camera_stream": {
       "type": "string",
-      "description": "The stream name to ask the gateway's stream_base_url for, when this printer has a camera the gateway could restream. Absent means no stream: either the printer reports no camera source, or it is a model whose camera is not reachable this way. That second case is the common one today - a Bambu P1/A1 does not publish an RTSP URL at all (confirmed: a P1P's ipcam block has ipcam_dev and ipcam_record and no rtsp_url), and only the X1/H2 class does. Those need Bambu's proprietary port-6000 JPEG stream instead, which is a separate client this gateway does not have yet."
+      "description": "The stream name to ask the gateway's stream_base_url for, when this printer has a camera the gateway could restream. Absent means no stream: either the printer reports no camera source, or it is a model whose camera is not reachable this way. That second case is the common one today - a Bambu P1/A1 does not publish an RTSP URL at all (confirmed: a P1P's ipcam block has ipcam_dev and ipcam_record and no rtsp_url), and only the X1/H2 class does. Those are served by camera_snapshot instead."
+    },
+    "camera_snapshot": {
+      "type": "boolean",
+      "description": "True when this printer's camera can only be read as single JPEG frames (a Bambu P1/A1: proprietary TLS stream on port 6000, no RTSP) and the gateway will answer a CameraSnapshotRequest for it. Mutually exclusive with camera_stream in practice. Absent means false."
     }
   },
   "required": [

schemas/continuum/v1/edge/server_message.schema.json

@@ -110,6 +110,18 @@
       ],
       "additionalProperties": false
     },
+    {
+      "type": "object",
+      "title": "CameraSnapshotRequest",
+      "description": "Read one JPEG frame from a printer's camera and send it back as a CameraSnapshot. For the printers whose camera is not RTSP (Bambu P1/A1, telemetry camera_snapshot true). Unlike WebrtcOffer this DOES carry the picture through the cloud, which is acceptable only because the frames are small, low-rate and requested one at a time.",
+      "properties": {
+        "type": { "const": "camera_snapshot_request" },
+        "request_id": { "type": "string" },
+        "printer_id": { "type": "string", "description": "The gateway's own printer id." }
+      },
+      "required": ["type", "request_id", "printer_id"],
+      "additionalProperties": false
+    },
     {
       "type": "object",
       "title": "ProvisionPrinter",