feat(proxmox): add LXC container stats endpoint with streaming support

Implement a new API endpoint to retrieve real-time statistics for Proxmox
LXC containers, similar to `docker stats` functionality.

Changes:
- Add `GET /api/v1/proxmox/stats/:node/:vmid` endpoint with HTTP and WebSocket support
- Implement resource polling loop to cache VM metadata every 3 seconds
- Create `LXCStats()` method with streaming (websocket) and single-shot modes
- Format output as: STATUS|CPU%|MEM USAGE/LIMIT|MEM%|NET I/O|BLOCK I/O
- Add `GetResource()` method for efficient VM resource lookup by kind and ID
- Fix task creation bug using correct client reference

Example response:
  running|31.1%|9.6GiB/20GiB|48.87%|4.7GiB/3.3GiB|25GiB/36GiB

internal/api/v1/docs/swagger.yaml

@@ -2119,6 +2119,10 @@ paths:
           description: Unauthorized
           schema:
             $ref: '#/definitions/ErrorResponse'
+        "404":
+          description: Node not found
+          schema:
+            $ref: '#/definitions/ErrorResponse'
         "500":
           description: Internal server error
           schema:
@@ -2128,6 +2132,49 @@ paths:
       - proxmox
       - websocket
       x-id: journalctl
+  /api/v1/proxmox/stats/{node}/{vmid}:
+    get:
+      consumes:
+      - application/json
+      description: Get proxmox stats in format of "STATUS|CPU%%|MEM USAGE/LIMIT|MEM%%|NET
+        I/O|BLOCK I/O"
+      parameters:
+      - in: path
+        name: node
+        required: true
+        type: string
+      - in: path
+        name: vmid
+        required: true
+        type: integer
+      produces:
+      - application/json
+      responses:
+        "200":
+          description: Stats output
+          schema:
+            type: string
+        "400":
+          description: Invalid request
+          schema:
+            $ref: '#/definitions/ErrorResponse'
+        "403":
+          description: Unauthorized
+          schema:
+            $ref: '#/definitions/ErrorResponse'
+        "404":
+          description: Node not found
+          schema:
+            $ref: '#/definitions/ErrorResponse'
+        "500":
+          description: Internal server error
+          schema:
+            $ref: '#/definitions/ErrorResponse'
+      summary: Get proxmox stats
+      tags:
+      - proxmox
+      - websocket
+      x-id: stats
   /auth/callback:
     post:
       description: Handles the callback from the provider after successful authentication