feat: Windows-native desktop polish (tray, single-instance, deep links, Mica, installer)

- System tray with Open/Quit menu + left-click toggle; closing the window now
  minimizes to tray instead of quitting, so notifications keep arriving.
- Single-instance: a second launch focuses the running window (and forwards a
  matrix: link) instead of colliding on the localhost port.
- Window: 1100x720 default, 480x600 min, centered first run; starts hidden and
  shows on page-load to kill the white launch flash (8s failsafe).
- matrix: deep links via tauri-plugin-deep-link -> dispatched to the web client
  (useDeepLinkNavigate) for both cold-start and already-running cases.
- Windows 11 Mica backdrop (subtle; app paints opaque TDS bg).
- NSIS installer: per-user install (no UAC), downloadBootstrapper.
- Remove dead/broken src/menu.rs.
- Bump cinny submodule to 053b364a (deep-link web handler).

Note: Rust not compiled locally (no toolchain / Windows-only paths); verified by
careful API review against tauri 2.10 — needs a real 'tauri build' to confirm.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src-tauri/tauri.conf.json

@@ -6,6 +6,12 @@
       "certificateThumbprint": null,
       "digestAlgorithm": "sha256",
       "timestampUrl": "",
+      "webviewInstallMode": {
+        "type": "downloadBootstrapper"
+      },
+      "nsis": {
+        "installMode": "currentUser"
+      },
       "wix": {
         "bannerPath": "wix/banner.bmp",
         "dialogImagePath": "wix/dialogImage.bmp"
@@ -55,6 +61,11 @@
       "endpoints": [
         "https://code.lotusguild.org/LotusGuild/cinny-desktop/releases/download/latest/release.json"
       ]
+    },
+    "deep-link": {
+      "desktop": {
+        "schemes": ["matrix"]
+      }
     }
   },
   "app": {