feat: dedicated ports per panel tier (8880/8881/8882)

Each panel now has its own dedicated port and is fully self-contained:
- Port 8880: User panel (end-user hosting dashboard)
- Port 8881: Reseller panel (account/package management)
- Port 8882: Admin panel (datacenter/server manager)

Changes:
- install.sh: PORT_USER/PORT_RESELLER/PORT_ADMIN constants; three separate
  nginx/Apache vhosts; UFW opens all three ports; Fail2Ban jail per port;
  credentials file shows all three URLs
- config.ini: stores port_user/port_reseller/port_admin
- Core.php: defines PORT_USER/RESELLER/ADMIN, detects CURRENT_PORTAL from
  SERVER_PORT so the API knows which tier is being accessed
- Auth.php: portalUrl() maps role → correct port for cross-portal redirects
- auth.php endpoint: returns portal_url on login so JS redirects to right port
- index.php login: uses portal_url from API response (no hardcoded paths)
- admin/index.php: inline login form (port 8882 is self-contained, no redirect)
- user/index.php: inline login form (port 8880 self-contained)
- reseller/index.php: new full reseller panel with inline login (port 8881);
  sidebar with accounts, packages, DNS, branding, bandwidth report sections

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

panel/public/index.php

@@ -96,8 +96,8 @@ document.getElementById('login-form').addEventListener('submit', async e => {
     const data = await res.json();
     if (!data.success) throw new Error(data.message || 'Login failed');
 
-    const role = data.data.user.role;
-    const dest = REDIRECT || (role === 'admin' ? '/admin/' : role === 'reseller' ? '/reseller/' : '/user/');
+    // Each role redirects to its dedicated port
+    const dest = REDIRECT || data.data.portal_url || '/';
     location.href = dest;
   } catch (ex) {
     err.textContent = ex.message;