feat(web): AlbumModal follow everywhere + Settings polish (#10)

Follow affordance in ALL album modals (user request): thread artistMbid through
the remaining callers — Library, Wanted, and artist Discography. /api/library
and /api/wanted now expose artistMbid (from the joined MonitoredRelease); the
artist-detail route already exposed mbid. So every album modal now links the
artist name to their page + shows a Follow/Following button.

Settings polish (#10):
- Qobuz tab: drop the email/password inputs (the engine prefers the more
  reliable user-id + auth-token path); a "Clear legacy login" affordance appears
  only when old email/password creds are still stored, and the PUT no longer
  sends them.
- Clear-button alignment fixed: .field label is a flex row and .field-grid
  bottom-aligns inputs, so a set-secret field (with its · set + Clear) lines up
  with a plain sibling field.
- Library tab gains a read-only Staging path panel (/staging, STAGING_DIR, why
  fast local disk, rebuild-to-change).
- Monitor + Discovery tabs gain grounded helptext (quality-class 1/2/3 cutoff,
  poll/retry/upgrade-window; sweep cadence + seeds-per-chunk + ListenBrainz URL).

web 152 tests, tsc + build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/src/app/wanted/wanted-client.tsx

@@ -10,6 +10,7 @@ import { toast } from "../_ui/toast";
 type Wanted = {
   id: string;
   artistName: string;
+  artistMbid: string | null;
   album: string;
   state: string;
   currentQualityClass: number | null;
@@ -124,6 +125,7 @@ export function WantedClient() {
             artist: open.artistName,
             year: open.firstReleaseDate?.slice(0, 4) ?? null,
             type: open.primaryType,
+            artistMbid: open.artistMbid,
           }}
           status={<span className="chip working">{stateLabel(open)}</span>}
           actions={