Redesign app with new UI kit

Redesign the entire app with a new UI kit. Typography, colors, icons,
avatars, and border radii have all been updated for a more polished,
consistent appearance that matches our other products like
radicle-explorer.

- Replace blockies-based avatars with a new DID-based avatar system
- Move Settings and Create Issue into fullscreen modals
- Change the default theme to follow the system theme
- Remove window decorations on macOS for a cleaner, more native feel
- Update the app icon
- Fix popovers and tooltips

Navigation:

- Rewrite app navigation and layouts
- Add a sidebar that gives you access to all your repos
- Change the startup screen to open directly to the notification inbox
- Add a getting started guide shown to new users on first launch

Settings:

- Add a setting to disable the notification badge
- Add a code font setting

Bug fixes:

- Fix reactions and edits incorrectly targeting the root comment
  instead of the intended reply
- Restrict issue/patch state, labels and assignees to delegates only

package.json

@@ -25,6 +25,7 @@
   },
   "license": "GPL-3.0-only",
   "dependencies": {
+    "@floating-ui/dom": "^1.7.6",
     "@tauri-apps/api": "^2.5.0",
     "@tauri-apps/plugin-clipboard-manager": "^2.2.2",
     "@tauri-apps/plugin-dialog": "^2.2.1",