Dashboard account section, profile API, and CSS account panels

- SSO session auth gating on all protected pages
- dashboard.php: account section (profile form + workspace panel),
  onboarding prompt modal, overview bar extracted to CSS classes,
  dashboard.css linked in page head
- api/profile.php: save/dismiss endpoint for optional profile fields
- assets/css/dashboard.css: account grid, dash-account-panel,
  dash-profile-form, profile-prompt-backdrop modal, overview bar
  classes, dash-section-kicker, dash-tier-badge base styles
- includes/bootstrap.php: dbnToolsMainUserProfile,
  dbnToolsProfileNeedsPrompt, dbnToolsRequirePageAuth
- scripts/sql/004_user_profile_fields.sql: nullable phone, address,
  and profile_prompt_dismissed_at columns

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

includes/layout.php

@@ -4,6 +4,9 @@ declare(strict_types=1);
 require_once __DIR__ . '/bootstrap.php';
 
 $layoutIsGuest = !dbnToolsIsAuthenticated();
+if ($layoutIsGuest) {
+    dbnToolsRequirePageAuth($_SERVER['REQUEST_URI'] ?? '/dashboard.php');
+}
 
 $uiLang = dbnToolsCurrentLanguage();
 $navItems = dbnToolsLaunchedTools($uiLang);