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/hooks/useScanPolling.ts

@@ -0,0 +1,64 @@
+import { useEffect } from 'react';
+import { getScanStatus } from '../api/subsonicScan';
+import { useScanStore } from '../store/scanStore';
+import { useAuthStore } from '../store/authStore';
+import { serverListDisplayLabel } from '../utils/server/serverDisplayName';
+import { showToast } from '../utils/ui/toast';
+import i18n from '../i18n';
+
+const POLL_MS = 2000;
+const JUST_FINISHED_HOLD_MS = 2500;
+
+/**
+ * Polls `getScanStatus` on each server whose scan was triggered from the app.
+ * Lives at the app root so dismissing the dropdown doesn't stop the poll.
+ */
+export function useScanPolling() {
+  useEffect(() => {
+    let cancelled = false;
+    const inFlight = new Set<string>();
+
+    const tick = async () => {
+      if (cancelled) return;
+      const { byServer, set } = useScanStore.getState();
+      const runningIds = Object.entries(byServer)
+        .filter(([, e]) => e.phase === 'starting' || e.phase === 'running')
+        .map(([id]) => id);
+
+      await Promise.all(runningIds.map(async serverId => {
+        if (inFlight.has(serverId)) return;
+        inFlight.add(serverId);
+        try {
+          const status = await getScanStatus(serverId);
+          if (cancelled) return;
+          const current = useScanStore.getState().byServer[serverId];
+          if (!current) return;
+
+          if (status.scanning) {
+            set(serverId, { phase: 'running', count: status.count });
+          } else {
+            // Scan finished — show check briefly, then auto-clear.
+            set(serverId, { phase: 'just-finished', count: status.count });
+            const servers = useAuthStore.getState().servers;
+            const srv = servers.find(s => s.id === serverId);
+            const name = srv ? serverListDisplayLabel(srv, servers) : serverId;
+            showToast(i18n.t('settings.scan.toast', { name, count: status.count }), 4000, 'success');
+            setTimeout(() => {
+              const after = useScanStore.getState().byServer[serverId];
+              if (after?.phase === 'just-finished') {
+                useScanStore.getState().clear(serverId);
+              }
+            }, JUST_FINISHED_HOLD_MS);
+          }
+        } catch {
+          if (!cancelled) set(serverId, { phase: 'error' });
+        } finally {
+          inFlight.delete(serverId);
+        }
+      }));
+    };
+
+    const interval = setInterval(tick, POLL_MS);
+    return () => { cancelled = true; clearInterval(interval); };
+  }, []);
+}