Add login modal to landing page

- Show login modal when user is not authenticated
- Add handleLogin, showLoginModal, closeLoginModal functions
- Add login modal HTML with username/password form
- Add CSS styles for modal

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

public/claude-landing.html

@@ -65,6 +65,30 @@
         </div>
     </section>
 
+    <!-- Login Modal -->
+    <div id="login-modal" class="modal" style="display: none;">
+        <div class="modal-content">
+            <div class="modal-header">
+                <h2>Login to Claude Code</h2>
+                <button class="modal-close" onclick="closeLoginModal()">&times;</button>
+            </div>
+            <div class="modal-body">
+                <form id="login-form" onsubmit="handleLogin(event)">
+                    <div class="form-group">
+                        <label for="login-username">Username:</label>
+                        <input type="text" id="login-username" name="username" required autofocus>
+                    </div>
+                    <div class="form-group">
+                        <label for="login-password">Password:</label>
+                        <input type="password" id="login-password" name="password" required>
+                    </div>
+                    <div id="login-error" class="login-error" style="display: none;"></div>
+                    <button type="submit" class="btn-primary">Login</button>
+                </form>
+            </div>
+        </div>
+    </div>
+
     <script src="/claude/claude-ide/error-monitor.js"></script>
     <script src="/claude/js/app.js"></script>
     <script src="/claude/claude-ide/projects-landing.js"></script>