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/locales/zh/settings.ts

@@ -22,6 +22,8 @@ export const settings = {
   serverPassword: '密码',
   addServer: '添加服务器',
   addServerTitle: '添加新服务器',
+  editServer: '编辑',
+  editServerTitle: '编辑服务器',
   useServer: '使用',
   deleteServer: '删除',
   noServers: '未保存任何服务器。',
@@ -459,4 +461,16 @@ export const settings = {
   floatingPlayerBarSub: '保持播放栏悬浮在内容上方',
   uiScaleTitle: '界面缩放',
   uiScaleLabel: '缩放',
+  scan: {
+    quick: '快速扫描',
+    full: '完整扫描',
+    quickTip: '快速扫描 — 仅索引新增/变更文件',
+    fullTip: '完整扫描 — 重新索引全部',
+    confirmFull: '再次点击确认',
+    confirmFullShort: '确认完整扫描',
+    scanning: '扫描中…',
+    done: '扫描完成',
+    error: '扫描失败',
+    toast: '{{name}}: 扫描完成 — 已索引 {{count}} 首曲目',
+  },
 };