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/styles/components/connection-indicator.css

@@ -83,3 +83,55 @@
   white-space: nowrap;
 }
 
+/* ─ Server scan actions (used in server switcher + settings card) ─ */
+.server-scan-actions--compact {
+  display: inline-flex;
+  align-items: center;
+  gap: 2px;
+  flex-shrink: 0;
+}
+
+.server-scan-btn--confirm {
+  background: var(--danger, #dc3c3c) !important;
+  color: #fff !important;
+  animation: server-scan-confirm-pulse 0.7s ease-in-out infinite alternate;
+}
+
+@keyframes server-scan-confirm-pulse {
+  from { filter: brightness(1); }
+  to   { filter: brightness(1.25); }
+}
+
+.server-scan-slot {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 28px;
+  height: 28px;
+}
+
+.server-scan-status {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  color: var(--text-muted);
+  font-size: 11px;
+  font-weight: 500;
+}
+
+.server-scan-status--done { color: var(--positive, #4ade80); }
+.server-scan-status--error { color: var(--danger, #dc3c3c); }
+
+.server-scan-status-count {
+  font-variant-numeric: tabular-nums;
+}
+
+/* Server card actions collapse to icon-only on narrow viewports — labels
+ * remain available as native tooltips via the existing `data-tooltip` /
+ * `aria-label` attributes. Breakpoint is tuned to where the action row
+ * starts overflowing on the default Settings layout. */
+@media (max-width: 1100px) {
+  .server-card-btn-label {
+    display: none;
+  }
+}