Add editing existing integrations, so an expired secret can be rotated

Manage integrations only supported add/toggle/delete — fixing an
expired API token meant deleting and recreating the whole integration.

- New GET /api/integrations/:id/config returns only the non-secret
  config fields (never the decrypted secret) so an edit form can
  pre-fill URL/tailnet/etc. fields.
- New POST /api/integrations/:id/test merges the stored, decrypted
  config with any freshly-typed overrides and pings the real adapter —
  lets "Test connection" work during an edit without ever sending the
  current secret back to the browser.
- New IntegrationEditForm component: secret fields render blank with a
  "leave blank to keep the current value" placeholder; submitting only
  sends the fields that were actually filled in, so a name/URL edit
  can't accidentally wipe a secret and a secret rotation can't touch
  anything else. Reuses the existing PATCH /:id route, which already
  merged partial config updates correctly.

Verified end-to-end against the real dev server: confirmed via direct
DB decryption that a non-secret-only edit leaves the stored secret
byte-for-byte unchanged, and that a secret-only edit rotates it without
touching other config; the test route was confirmed to make a real
network call (got a genuine "API token invalid" from Tailscale's API
against a fake key).

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

web/src/pages/Integrations.tsx

@@ -16,6 +16,7 @@ import {
   type TailscaleDevicesResponse,
 } from "../api/client";
 import IntegrationForm from "../components/IntegrationForm";
+import IntegrationEditForm from "../components/IntegrationEditForm";
 
 function proxmoxStatusBadge(status: string) {
   return status === "running" ? (
@@ -135,6 +136,7 @@ export default function Integrations({ user }: { user: CurrentUser }) {
 
   const [integrations, setIntegrations] = useState<IntegrationSummary[] | null>(null);
   const [managing, setManaging] = useState(false);
+  const [editingIntegration, setEditingIntegration] = useState<IntegrationSummary | null>(null);
   const [selectedId, setSelectedId] = useState<number | null>(null);
   const [error, setError] = useState<string | null>(null);
 
@@ -388,7 +390,18 @@ export default function Integrations({ user }: { user: CurrentUser }) {
 
       {managing ? (
         <>
-          <IntegrationForm onCreated={loadIntegrations} onCancel={() => setManaging(false)} />
+          {editingIntegration ? (
+            <IntegrationEditForm
+              integration={editingIntegration}
+              onSaved={() => {
+                setEditingIntegration(null);
+                loadIntegrations();
+              }}
+              onCancel={() => setEditingIntegration(null)}
+            />
+          ) : (
+            <IntegrationForm onCreated={loadIntegrations} onCancel={() => setManaging(false)} />
+          )}
           <div className="card">
             <div className="table-responsive">
               <table className="table table-vcenter card-table">
@@ -414,9 +427,14 @@ export default function Integrations({ user }: { user: CurrentUser }) {
                         </button>
                       </td>
                       <td>
-                        <button className="btn btn-sm btn-outline-danger" onClick={() => removeIntegration(i)}>
-                          Delete
-                        </button>
+                        <div className="btn-list flex-nowrap">
+                          <button className="btn btn-sm" onClick={() => setEditingIntegration(i)}>
+                            Edit
+                          </button>
+                          <button className="btn btn-sm btn-outline-danger" onClick={() => removeIntegration(i)}>
+                            Delete
+                          </button>
+                        </div>
                       </td>
                     </tr>
                   ))}