feat(servers): scan actions + edit existing server profiles (#780)

* feat(server-scan): plumbing for triggering library scans

Adds `startScan` / `getScanStatus` against the Subsonic API
(`fullScan=true` is Navidrome's extension), a small per-server scan
store, and a global polling hook (2 s cadence) that emits a toast when
each scan finishes. Scans can run on any configured server, including
inactive ones, by reusing `apiForServer`.

UI surfaces follow in the next commit.

* feat(server-scan): expose Quick / Full Scan in switcher + settings cards

Adds a `ServerScanActions` component with two variants (compact for the
server-switcher dropdown, card for the Settings server cards) backed by
the scan store from the previous commit. Full Scan requires a second
click within 3 s to confirm, matching the playlist-delete pattern.
Status slot shows a spinner with running track count while scanning, a
green check when finished, and a red icon on error.

The switcher row is converted from a single button to a flex container
so per-server scan controls don't hijack the server-switch click.
i18n added across all 9 locales.

* fix(server-scan): reorder switcher row to check / name / scan actions

Moves the check / spinner slot from the right edge to the left so the
spinner pop-in on server switch doesn't sit next to the scan icons.
Removes the layout shift that briefly hovered the Quick scan button
when the row re-rendered.

* feat(servers): edit existing server profiles in Settings → Servers

* Pencil-button on each server card opens an inline edit form that
  replaces the card (prefilled name / URL / username / password).
* `AddServerForm` reused with an `editingServer` prop — title flips to
  "Edit Server", submit label to "Save", magic-string field hidden (the
  edit scope is manual fields; magic-string remains an add-time invite
  shortcut).
* Edit saves unconditionally — ping runs post-save as a status indicator
  (analog to the existing Test button) instead of gating the save. Lets
  users update a profile when the server is currently unreachable.
* Translations across all 9 locales (`editServer`, `editServerTitle`).

* fix(servers): submit Add/Edit Server form on Enter

Wrapped the form body in a real <form>, made the submit button
type="submit", marked Cancel as type="button" so Enter no longer
cancels. Add-Mode now also responds to Enter — same flow, consistent
across both modes.

* fix(servers): collapse card action buttons to icon-only on narrow screens

* Quick-Scan / Full-Scan / Test buttons in each server card hide their
  text label below 1100px viewport via the .server-card-btn-label class
  and a single media query in connection-indicator.css.
* Labels remain accessible via data-tooltip and aria-label so screen
  readers + hover both keep working in the collapsed state.
* No content reflow above the breakpoint — pure additive CSS.

* fix(servers): include Use button in icon-only narrow-screen collapse

The Use ("Verwenden") button on inactive server cards lacked the
.server-card-btn-label wrapper, so its text stayed visible at narrow
viewports and pushed Edit/Delete off-screen. Added a Power icon and
wrapped the label so it collapses alongside the other action buttons.

* docs(changelog,credits): #780 server scan + edit

src/components/settings/AddServerForm.tsx

@@ -15,13 +15,20 @@ export function AddServerForm({
   onSave,
   onCancel,
   initialInvite = null,
+  editingServer = null,
 }: {
   onSave: (data: Omit<ServerProfile, 'id'>) => void;
   onCancel: () => void;
   initialInvite?: ServerMagicPayload | null;
+  editingServer?: ServerProfile | null;
 }) {
   const { t } = useTranslation();
-  const [form, setForm] = useState({ name: '', url: '', username: '', password: '' });
+  const isEdit = editingServer != null;
+  const [form, setForm] = useState(
+    editingServer
+      ? { name: editingServer.name, url: editingServer.url, username: editingServer.username, password: editingServer.password }
+      : { name: '', url: '', username: '', password: '' },
+  );
   const [magicString, setMagicString] = useState('');
   const [showPass, setShowPass] = useState(false);
   const [blockPasswordReveal, setBlockPasswordReveal] = useState(false);
@@ -85,8 +92,14 @@ export function AddServerForm({
   };
 
   return (
-    <div className="settings-card" style={{ marginTop: '1rem' }}>
-      <h3 style={{ fontWeight: 600, marginBottom: '1rem', fontSize: '14px' }}>{t('settings.addServerTitle')}</h3>
+    <form
+      className="settings-card"
+      style={{ marginTop: '1rem' }}
+      onSubmit={e => { e.preventDefault(); submit(); }}
+    >
+      <h3 style={{ fontWeight: 600, marginBottom: '1rem', fontSize: '14px' }}>
+        {isEdit ? t('settings.editServerTitle') : t('settings.addServerTitle')}
+      </h3>
       <div className="form-group" style={{ marginBottom: '0.75rem' }}>
         <label style={{ fontSize: 13 }}>{t('settings.serverName')}</label>
         <input className="input" type="text" value={form.name} onChange={update('name')} placeholder="My Navidrome" autoComplete="off" />
@@ -142,26 +155,25 @@ export function AddServerForm({
           )}
         </div>
       </div>
-      <div className="form-group" style={{ marginBottom: '0.75rem' }}>
-        <label style={{ fontSize: 13 }}>{t('login.orMagicString')}</label>
-        <input
-          className="input"
-          type="text"
-          value={magicString}
-          onChange={handleMagicStringChange}
-          placeholder={t('login.magicStringPlaceholder')}
-          autoComplete="off"
-        />
-      </div>
+      {!isEdit && (
+        <div className="form-group" style={{ marginBottom: '0.75rem' }}>
+          <label style={{ fontSize: 13 }}>{t('login.orMagicString')}</label>
+          <input
+            className="input"
+            type="text"
+            value={magicString}
+            onChange={handleMagicStringChange}
+            placeholder={t('login.magicStringPlaceholder')}
+            autoComplete="off"
+          />
+        </div>
+      )}
       <div style={{ display: 'flex', gap: '8px', justifyContent: 'flex-end' }}>
-        <button className="btn btn-ghost" onClick={onCancel}>{t('common.cancel')}</button>
-        <button
-          className="btn btn-primary"
-          onClick={submit}
-        >
-          {t('common.add')}
+        <button type="button" className="btn btn-ghost" onClick={onCancel}>{t('common.cancel')}</button>
+        <button type="submit" className="btn btn-primary">
+          {isEdit ? t('common.save') : t('common.add')}
         </button>
       </div>
-    </div>
+    </form>
   );
 }