fix: merge main, address code review feedback for security fix PR #816

- Merge origin/main into branch (resolve conflict in integrations_dashboard.html)
- Add defensive JSON parsing with try/except for integration.config
- Wrap tester() call in try/except to prevent 500 errors from bad config
- Add i18n key integrations.connection_test_failed_fallback in en.json
- Reference i18n key in template JS fallback message
- Update SECURITY_AUDIT.md: add fix date (2026-03-23), update doc date
- Remove accidental revert.sh file
- Fix missing MagicMock/patch imports in test file
- Add tests for invalid JSON config and tester exception error paths

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/DocuElevate/sessions/daebb70e-059a-4601-8864-88eef49f99cf

frontend/templates/signup.html

@@ -4,7 +4,7 @@
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <title>DocuElevate - Create Account</title>
-    <link href="https://cdn.jsdelivr.net/npm/tailwindcss@2.2.19/dist/tailwind.min.css" rel="stylesheet">
+    <link rel="stylesheet" href="/static/styles.css" />
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css"
           integrity="sha512-DTOQO9RWCH3ppGqcWaEA1BIZOC6xxalwEsw9c2QQeAIftl+Vegovlnee1c9QX4TctnWMn13TZye+giMm8e2LwA=="
           crossorigin="anonymous" referrerpolicy="no-referrer" />
@@ -32,6 +32,14 @@
                 error: '',
                 async submit() {
                     this.error = '';
+                    if (this.username.length < 3 || this.username.length > 64) {
+                        this.error = 'Username must be between 3 and 64 characters.';
+                        return;
+                    }
+                    if (!/^[a-zA-Z0-9_-]+$/.test(this.username)) {
+                        this.error = 'Username may only contain letters, numbers, hyphens, and underscores. Dots and other special characters are not allowed.';
+                        return;
+                    }
                     if (this.password !== this.password_confirm) {
                         this.error = 'Passwords do not match.';
                         return;
@@ -58,7 +66,12 @@
                             }
                         } else {
                             const data = await resp.json();
-                            this.error = data.detail || 'Registration failed. Please try again.';
+                            const detail = data.detail;
+                            if (Array.isArray(detail)) {
+                                this.error = detail.map(e => e.msg || String(e)).join(' ') || 'Registration failed. Please try again.';
+                            } else {
+                                this.error = detail || 'Registration failed. Please try again.';
+                            }
                         }
                     } catch(e) {
                         this.error = 'Network error. Please try again.';