Search Deezer and MusicBrainz together; add preview clips

Search
- Albums and songs search Deezer and MusicBrainz at once and merge the
  results: duplicates keep the Deezer copy, best word matches first.
  Deezer's search misses albums it carries (Death Magnetic) and most game
  soundtracks; MusicBrainz finds them
- MusicBrainz secondary types are shown ("Soundtrack", "Live")
- Settings: Deezer + MusicBrainz (default), Deezer only, MusicBrainz only
- Search results show which service they came from

Previews
- Songs and albums get a play button (cards, rows, detail view, editor,
  and Deezer search results) for a 30-second Deezer clip; albums play
  their most popular track
- Clips are looked up fresh (Deezer URLs expire), cached 10 minutes, and
  streamed through Canon with Range support; hidden lists stay private
- Entries from MusicBrainz or added by hand are matched to Deezer on save
  so they can preview too
- "Play previews" toggle in Settings → Profile

Tests cover merging and title/artist matching; `-tags live` runs checks
against the real services.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/static/js/public.js

@@ -1,5 +1,6 @@
 // Public pages: item detail dialog and grid/list toggle.
 import { h, icon, openDialog, storageGet, storageSet } from "./common.js";
+import { previewButton } from "./player.js";
 
 // Each ranked list on the page ships its items as JSON next to the markup.
 const lists = [...document.querySelectorAll("[data-items]")].map((ol) => {
@@ -45,6 +46,7 @@ function renderDialog(list, idx) {
         h("h3", {}, "About"),
         h("p", { class: "dlg-desc" }, it.description)),
       h("div", { class: "dlg-actions" },
+        it.preview && previewButton(`/preview/${it.id}`, `Play a preview of ${it.title}`, "play-btn play-btn--inline"),
         it.link && h("a", { class: "btn btn--sm", href: it.link, target: "_blank", rel: "noopener noreferrer" },
           icon("external"), it.source ? `View on ${it.source}` : "Learn more"),
         h("div", { class: "dlg-nav" }, prev, next),