feat(tauri-app): Tauri 2 capabilities default + open_devtools in debug

The dev build was missing a capabilities/default.json so the
event:listen and notification:is-permission-granted plugins
denied every IPC call from main.ts (logged as 'event.listen not
allowed' etc. in DevTools). Add the minimum set needed by
client.ts / main.ts and the AppView/Tauri commands registered
in lib.rs.

Also open the webview devtools automatically on startup behind
a debug_assertions guard, so the frontend console + DOM inspector
are available without reaching for the macOS View menu.

crates/tauri-app/src-tauri/capabilities/default.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "default",
+  "description": "Default capabilities for the maarcadetweet main window",
+  "windows": ["main"],
+  "permissions": [
+    "core:default",
+    "core:event:default",
+    "core:webview:allow-internal-toggle-devtools",
+    "core:window:default",
+    "notification:default",
+    "shell:default",
+    "dialog:default",
+    "updater:default",
+    "window-state:default"
+  ]
+}