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/store/scanStore.ts

@@ -0,0 +1,33 @@
+import { create } from 'zustand';
+
+export type ScanPhase = 'idle' | 'starting' | 'running' | 'just-finished' | 'error';
+
+export interface ScanEntry {
+  phase: ScanPhase;
+  type: 'quick' | 'full';
+  count: number;
+  /** Set while user is in "press again to confirm" state for a full scan. */
+  confirmingFull: boolean;
+}
+
+const EMPTY: ScanEntry = { phase: 'idle', type: 'quick', count: 0, confirmingFull: false };
+
+interface ScanState {
+  byServer: Record<string, ScanEntry>;
+  get: (serverId: string) => ScanEntry;
+  set: (serverId: string, patch: Partial<ScanEntry>) => void;
+  clear: (serverId: string) => void;
+}
+
+export const useScanStore = create<ScanState>((set, getState) => ({
+  byServer: {},
+  get: (serverId) => getState().byServer[serverId] ?? EMPTY,
+  set: (serverId, patch) => set(s => ({
+    byServer: { ...s.byServer, [serverId]: { ...(s.byServer[serverId] ?? EMPTY), ...patch } },
+  })),
+  clear: (serverId) => set(s => {
+    const next = { ...s.byServer };
+    delete next[serverId];
+    return { byServer: next };
+  }),
+}));