Move Dockhand container management to its own top-level Docker page

Container management was buried inside the generic Integrations
browsing view, mixed in with five unrelated integration types behind
a single "pick any integration" dropdown. Give it a dedicated page,
matching how Servers & Tasks and DNS already get their own top-level
spot instead of living inside Integrations.

New web/src/pages/Docker.tsx reuses the existing, unchanged Dockhand
API routes and adapter (no server changes) — it just has its own
integration picker scoped to Dockhand only, rather than sharing
Integrations' any-type dropdown. Added a Docker nav item (right after
Integrations) and route.

Removed the Dockhand-specific state/handlers/table from Integrations
entirely; adding, editing, enabling/disabling, and deleting the
Dockhand credential itself still happens under Integrations -> Manage
integrations like every other integration. Selecting a Dockhand row in
Integrations' generic browsing dropdown now points to the Docker page
instead of rendering a container table there too.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/layout/AppShell.tsx

@@ -7,6 +7,7 @@ import {
   IconNetwork,
   IconKey,
   IconPlugConnected,
+  IconBrandDocker,
   IconUsers,
   IconHistory,
   IconSettings,
@@ -28,6 +29,7 @@ const NAV_ITEMS: NavItem[] = [
   { to: "/ipam", label: "IP Addresses", icon: <IconNetwork size={20} /> },
   { to: "/secrets", label: "Secrets", icon: <IconKey size={20} /> },
   { to: "/integrations", label: "Integrations", icon: <IconPlugConnected size={20} /> },
+  { to: "/docker", label: "Docker", icon: <IconBrandDocker size={20} /> },
   { to: "/users", label: "Users", icon: <IconUsers size={20} />, minRole: "admin" },
   { to: "/audit-log", label: "Audit Log", icon: <IconHistory size={20} />, minRole: "operator" },
   { to: "/settings", label: "Settings", icon: <IconSettings size={20} />, minRole: "admin" },