feat(auth): implement authentication manager with email and OAuth support

- Added AuthManager class to handle user authentication and state management.
- Integrated Supabase for authentication, including email/password and OAuth providers (Google, GitHub, Apple).
- Implemented UI for authentication with options to sign in, sign up, and continue as guest.
- Added user avatar display and update functionality based on authentication state.
- Enhanced application initialization to show authentication screen on first run.
- Updated styles for user avatar and authentication UI components.

Author: murdercode

package-lock.json

@@ -16,6 +16,7 @@
   },
   "dependencies": {
     "@aptabase/tauri": "^0.4.1",
+    "@supabase/supabase-js": "^2.50.0",
     "@tauri-apps/api": "^2.5.0",
     "@tauri-apps/plugin-dialog": "^2.2.2",
     "@tauri-apps/plugin-notification": "^2",

package.json

@@ -39,6 +39,27 @@
     </div>
 
     <div class="sidebar-bottom">
+      <div class="user-avatar-container" id="user-avatar-container" style="display: none;">
+        <div class="user-avatar" id="user-avatar">
+          <img id="user-avatar-img" src="" alt="User Avatar" style="display: none;">
+          <div id="user-avatar-fallback" class="avatar-fallback">G</div>
+        </div>
+        <div class="user-info" id="user-info">
+          <span class="user-name" id="user-name">Guest</span>
+          <div class="user-actions">
+            <button class="user-action-btn" id="user-sign-out" title="Sign Out" style="display: none;">
+              <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5">
+                <path stroke-linecap="round" stroke-linejoin="round" d="M15.75 9V5.25A2.25 2.25 0 0013.5 3h-6a2.25 2.25 0 00-2.25 2.25v13.5A2.25 2.25 0 005.25 21h6a2.25 2.25 0 002.25-2.25V15m3 0l3-3m0 0l-3-3m3 3H9" />
+              </svg>
+            </button>
+            <button class="user-action-btn" id="user-sign-in" title="Sign In">
+              <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5">
+                <path stroke-linecap="round" stroke-linejoin="round" d="M15.75 6a3.75 3.75 0 11-7.5 0 3.75 3.75 0 017.5 0zM4.501 20.118a7.5 7.5 0 0114.998 0A17.933 17.933 0 0112 21.75c-2.676 0-5.216-.584-7.499-1.632z" />
+              </svg>
+            </button>
+          </div>
+        </div>
+      </div>
       <button class="sidebar-icon-large" id="settings-nav" data-view="settings" title="Settings">
         <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5">
           <path stroke-linecap="round" stroke-linejoin="round"