feat(desktop): Tauri mac shell around the web export

Black screen root cause: Tauri injects nonces into style-src, which
makes WebKit drop 'unsafe-inline' and block react-native-web's inline
style attributes. style-src is now excluded from CSP modification.
Window opens on the home screen so the section menu is reachable.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wmf3K9nCoEsXvvwkmMnuiM

desktop/src-tauri/capabilities/main.json

@@ -0,0 +1,7 @@
+{
+  "$schema": "../gen/schemas/desktop-schema.json",
+  "identifier": "main-capability",
+  "description": "Capabilities for the GTD main window. The Expo web frontend needs no Tauri plugin APIs — it only talks to the remote API over fetch — so this grants the read-only core defaults (window/event/app metadata) and nothing privileged.",
+  "windows": ["main"],
+  "permissions": ["core:default"]
+}