feat(desktop): add file attachments and native chat window

- Add file upload support in chat (PDF, images, txt, docs, xlsx)
  - Limited to 10MB max file size
  - Only allowed extensions for security
- Use native Windows decorations for chat window
- Remove ChatFloatingWidget (replaced by native window)
- Simplify chat event listeners (window managed by Rust)
- Fix typo "sessao" -> "sessão"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

bun.lock

@@ -105,6 +105,7 @@
         "@radix-ui/react-scroll-area": "^1.2.3",
         "@radix-ui/react-tabs": "^1.1.13",
         "@tauri-apps/api": "^2",
+        "@tauri-apps/plugin-dialog": "^2.4.2",
         "@tauri-apps/plugin-opener": "^2",
         "@tauri-apps/plugin-process": "^2",
         "@tauri-apps/plugin-store": "^2",
@@ -689,6 +690,8 @@
 
     "@tauri-apps/cli-win32-x64-msvc": ["@tauri-apps/cli-win32-x64-msvc@2.9.5", "", { "os": "win32", "cpu": "x64" }, "sha512-Vg50U74x1A4b2iBVtDcAVPbI1XVuzSmwlduuBM1VewxtRaVj5GDzWnYtBcnuIk+VGzNApRDfDhraAXGaW2a/Gw=="],
 
+    "@tauri-apps/plugin-dialog": ["@tauri-apps/plugin-dialog@2.4.2", "", { "dependencies": { "@tauri-apps/api": "^2.8.0" } }, "sha512-lNIn5CZuw8WZOn8zHzmFmDSzg5zfohWoa3mdULP0YFh/VogVdMVWZPcWSHlydsiJhRQYaTNSYKN7RmZKE2lCYQ=="],
+
     "@tauri-apps/plugin-opener": ["@tauri-apps/plugin-opener@2.5.2", "", { "dependencies": { "@tauri-apps/api": "^2.8.0" } }, "sha512-ei/yRRoCklWHImwpCcDK3VhNXx+QXM9793aQ64YxpqVF0BDuuIlXhZgiAkc15wnPVav+IbkYhmDJIv5R326Mew=="],
 
     "@tauri-apps/plugin-process": ["@tauri-apps/plugin-process@2.3.1", "", { "dependencies": { "@tauri-apps/api": "^2.8.0" } }, "sha512-nCa4fGVaDL/B9ai03VyPOjfAHRHSBz5v6F/ObsB73r/dA3MHHhZtldaDMIc0V/pnUw9ehzr2iEG+XkSEyC0JJA=="],