refactor!: remove redundant compatibility layers

Use native browser and Tauri behavior instead of custom selector, dialog, and window-state implementations. Remove obsolete bridge, relay, asset, and dependency paths to keep the supported surface small.

BREAKING CHANGE: The Noctalia relay no longer accepts --agent, and the Tauri host no longer exposes the legacy load_agent command.

ui/package-lock.json

@@ -11,7 +11,6 @@
       "dependencies": {
         "@tauri-apps/api": "^2",
         "@tauri-apps/plugin-dialog": "^2.7.2",
-        "@tauri-apps/plugin-opener": "^2",
         "react": "^19.1.0",
         "react-dom": "^19.1.0",
         "react-markdown": "^10.1.0",
@@ -1605,15 +1604,6 @@
         "@tauri-apps/api": "^2.11.0"
       }
     },
-    "node_modules/@tauri-apps/plugin-opener": {
-      "version": "2.5.4",
-      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-opener/-/plugin-opener-2.5.4.tgz",
-      "integrity": "sha512-1HnPkb+AmgO29HBazm4uPLKB+r7zzcTBW1d0fyYp1uP+jwtpoiNDGKMMzz58SFp49nOIrxdE3aUJtT57lfO9CQ==",
-      "license": "MIT OR Apache-2.0",
-      "dependencies": {
-        "@tauri-apps/api": "^2.11.0"
-      }
-    },
     "node_modules/@testing-library/dom": {
       "version": "10.4.1",
       "resolved": "https://registry.npmjs.org/@testing-library/dom/-/dom-10.4.1.tgz",