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/handler/content.rs

@@ -188,7 +188,7 @@ impl ApiHandler {
             }
         };
         let price_sats = match &item.access {
-            content_server::AccessControl::Paid { price_sats } => *price_sats,
+            content_server::AccessControl::Paid { price_sats, .. } => *price_sats,
             _ => {
                 // Not a paid item — no invoice to issue.
                 return Ok(build_response(
@@ -198,6 +198,13 @@ impl ApiHandler {
                 ));
             }
         };
+        if !content_server::method_accepted(&item.access, "lightning") {
+            return Ok(build_response(
+                StatusCode::BAD_REQUEST,
+                "application/json",
+                hyper::Body::from(r#"{"error":"The seller does not accept Lightning for this item"}"#),
+            ));
+        }
 
         let memo = format!("Archipelago peer file {content_id}");
         match self
@@ -315,7 +322,18 @@ impl ApiHandler {
             .unwrap_or_default();
         let price_sats = match catalog.items.iter().find(|i| i.id == content_id) {
             Some(i) => match &i.access {
-                content_server::AccessControl::Paid { price_sats } => *price_sats,
+                content_server::AccessControl::Paid { price_sats, .. } => {
+                    if !content_server::method_accepted(&i.access, "onchain") {
+                        return Ok(build_response(
+                            StatusCode::BAD_REQUEST,
+                            "application/json",
+                            hyper::Body::from(
+                                r#"{"error":"The seller does not accept on-chain payment for this item"}"#,
+                            ),
+                        ));
+                    }
+                    *price_sats
+                }
                 _ => {
                     return Ok(build_response(
                         StatusCode::BAD_REQUEST,