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>

core/archipelago/src/api/rpc/content.rs

@@ -179,7 +179,24 @@ impl RpcHandler {
                 if price == 0 {
                     return Err(anyhow::anyhow!("Paid content requires price_sats > 0"));
                 }
-                AccessControl::Paid { price_sats: price }
+                // Optional list of payment methods the sharer accepts.
+                // Absent/empty = all methods (backward compatible).
+                const KNOWN_METHODS: [&str; 4] = ["lightning", "onchain", "ecash", "fedimint"];
+                let accepted: Vec<String> = params
+                    .get("accepted_methods")
+                    .and_then(|v| v.as_array())
+                    .map(|arr| {
+                        arr.iter()
+                            .filter_map(|m| m.as_str())
+                            .filter(|m| KNOWN_METHODS.contains(m))
+                            .map(str::to_string)
+                            .collect()
+                    })
+                    .unwrap_or_default();
+                AccessControl::Paid {
+                    price_sats: price,
+                    accepted,
+                }
             }
             _ => return Err(anyhow::anyhow!("Invalid access type: {}", access_type)),
         };