feat(tauri): add Tauri v2 Android app wrapper

- Wrap apps/web as Android APK via Tauri v2 WebView (zero web changes)
- Disable default compression feature to avoid brotli/alloc-no-stdlib conflict with Rust 1.96
- Add RGBA icon placeholders
- Add Android keystore to gitignore

APK output: apps/tauri/gen/android/app/build/outputs/apk/

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

apps/tauri/tauri.conf.json

@@ -0,0 +1,30 @@
+{
+  "$schema": "https://raw.githubusercontent.com/tauri-apps/tauri/dev/crates/tauri-config-schema/schema.json",
+  "productName": "ZeaVis Edu",
+  "version": "0.1.0",
+  "identifier": "com.zeavis.edu",
+  "build": {
+    "frontendDist": "../web/dist",
+    "devUrl": "http://localhost:5173",
+    "beforeBuildCommand": "cd ../web && bun run build",
+    "beforeDevCommand": "cd ../web && bun run dev"
+  },
+  "app": {
+    "withGlobalTauri": false,
+    "windows": [
+      {
+        "title": "ZeaVis Edu",
+        "width": 800,
+        "height": 600
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all"
+  },
+  "plugins": {}
+}