feat(v2): Deno-first sidecar with Node.js fallback and signing key

Refactor SidecarManager to use SidecarCommand struct abstracting
runtime choice. resolve_sidecar_command() prefers Deno (runs TS
directly, no build step), falls back to Node.js if deno not in PATH.
Both runners bundled in tauri.conf.json resources. Set auto-update
signing pubkey in updater config.

v2/src-tauri/tauri.conf.json

@@ -30,7 +30,7 @@
         "https://github.com/DexterFromLab/BTerminal/releases/latest/download/latest.json"
       ],
       "dialog": true,
-      "pubkey": ""
+      "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IEJCRkZEMERDMTUwMzY5MjIKUldRaWFRTVYzTkQvdTYwRDh6YStaSE9rWUZYYkRGd3UvVUcydE1IQVdTM29uNTRPTlpjQmFqVFEK"
     }
   },
   "bundle": {
@@ -43,6 +43,10 @@
       "icons/icon.icns",
       "icons/icon.ico"
     ],
+    "resources": [
+      "../sidecar/agent-runner-deno.ts",
+      "../sidecar/dist/agent-runner.mjs"
+    ],
     "category": "DeveloperTool",
     "shortDescription": "Multi-session Claude agent dashboard",
     "longDescription": "BTerminal is a terminal emulator with integrated Claude AI agent sessions, SSH management, and a tiling pane layout. Built with Tauri, Svelte 5, and xterm.js.",