feat(content): seller-picked payment methods + music always in the bottom bar + video PiP

- Paid sharing: AccessControl::Paid gains an accepted-methods list
  (lightning/onchain/ecash/fedimint; empty = all, back-compat). Sellers pick
  methods in ShareModal, gated on what the node can actually receive (LND
  running/channel open, ecash wallet, fedimint joined) with an ⓘ that
  explains exactly how to enable a missing rail. Enforced server-side (the
  invoice/onchain mints refuse non-accepted methods; the serve gate only
  honors tokens/hashes for accepted rails) and the buyer's pay modal only
  offers what the seller accepts.
- Purchased music: the two remaining lightbox paths now use the bottom-bar
  player — the immediate post-ecash-purchase viewer and the Paid Files
  tab's window.open.
- Picture-in-picture buttons on the peer video player and the cloud media
  lightbox (utils/pip.ts; Chromium/Safari, no-op elsewhere).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/utils/pip.ts

@@ -0,0 +1,19 @@
+/** Video Picture-in-Picture helpers (Chromium/Safari; no-ops elsewhere).
+ *  Kiosk note: PiP is skipped on the WM-less kiosk X session by callers that
+ *  care — an unmanaged popup there is unusable (docs/tv-input-iframe-apps.md
+ *  sibling investigation, task #18). */
+
+export const pipSupported =
+  typeof document !== 'undefined' &&
+  'pictureInPictureEnabled' in document &&
+  document.pictureInPictureEnabled
+
+export async function togglePip(video: HTMLVideoElement | null | undefined): Promise<void> {
+  if (!video || !pipSupported) return
+  try {
+    if (document.pictureInPictureElement === video) await document.exitPictureInPicture()
+    else await video.requestPictureInPicture()
+  } catch {
+    // Permission/transient failure — the button is best-effort.
+  }
+}