Role isolation, impersonation, account ownership, loading spinners, Docker fixes

- Enforce portal role isolation: admin/reseller/user can only auth on their own port
- Admin/reseller impersonation: Login As with cookie handoff + Return banner in user panel
- Account ownership: admin can reassign accounts to resellers, DNS NS follows
- accounts/update: ownership change cascades package + NS to new owner
- users.php endpoint: admin list/filter by role (reseller dropdown)
- Docker launch fix: uDockerUpdateParams defined before call
- Nova.loading() spinners: login, SSL, PHP switch/save, backup create, docker launch/actions
- Logo consistency: gradient CPX text on all login pages, novacpx_logo_html() in all sidebars
- BackupManager: fix DB class name, table name, column name
- DNSManager: fix settings keys (ns1_hostname/ns2_hostname)
- docker.php: resolve account_id from user uid for all actions
- Auth: impersonate sets cookie + stores return_token for seamless round-trip

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

panel/public/reseller/index.php

@@ -56,7 +56,7 @@ $_pname = novacpx_panel_name('NovaCPX');
           <linearGradient id="rlgb" x1="12" y1="8" x2="28" y2="28"><stop offset="0%" stop-color="#6366f1"/><stop offset="100%" stop-color="#0ea5e9"/></linearGradient>
         </defs>
       </svg>
-      <div style="font-size:1.4rem;font-weight:700"><?= $_pname ?></div>
+      <div style="font-size:1.4rem;font-weight:300">Nova<strong style="font-weight:700;background:linear-gradient(135deg,#6366f1,#0ea5e9);-webkit-background-clip:text;-webkit-text-fill-color:transparent">CPX</strong></div>
       <div style="font-size:.78rem;color:var(--text-muted);margin-top:.25rem;text-transform:uppercase;letter-spacing:.1em">Reseller Panel</div>
     </div>
     <div class="card">