feat: streaming ecash payments + media playback overhaul

Cashu ecash protocol (BDHKE blind signatures, cashuA token format,
mint HTTP client) replacing the stub wallet. TollGate-inspired streaming
data payment system with step-based pricing (bytes/time/requests),
session management with incremental top-ups, usage metering, and
Nostr kind 10021 service advertisements.

13 new streaming.* RPC endpoints. Content server now verifies real
Cashu tokens. Profits tracking includes streaming revenue.

Frontend: GlobalAudioPlayer (persistent bottom bar across all pages),
video lightbox with full controls, audio in MediaLightbox, free file
previews (no blur), paid 10% audio/video previews, separated play
vs download buttons in PeerFiles.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/streaming/mod.rs

@@ -0,0 +1,39 @@
+//! Streaming ecash payments for metered data access.
+//!
+//! Implements a TollGate-inspired protocol for paying for streaming data
+//! using Cashu ecash micropayments. Supports three metering models:
+//!
+//! - **Bytes**: Pay per MB downloaded (content, federation sync)
+//! - **Time**: Pay per minute of access (relay, API endpoints)
+//! - **Requests**: Pay per API call
+//!
+//! # Architecture
+//!
+//! ```text
+//! Paying Node                          Selling Node
+//! ┌──────────────┐                     ┌──────────────────────┐
+//! │ Cashu Wallet  │──cashuA token──────▶│ Gate                 │
+//! │ (real BDHKE)  │                     │  verify + receive    │
+//! └──────────────┘                     └──────┬───────────────┘
+//!                                             │ create/topup session
+//!                                      ┌──────▼───────────────┐
+//!                                      │ Meter                 │
+//!                                      │  track usage          │
+//!                                      └──────┬───────────────┘
+//!                                             │ enforce allotment
+//!                                      ┌──────▼───────────────┐
+//!                                      │ Service               │
+//!                                      │  content / sync / api │
+//!                                      └──────────────────────┘
+//! ```
+//!
+//! # Discovery
+//!
+//! Services are advertised via Nostr kind 10021 events (TollGate TIP-01
+//! compatible) containing pricing tags per TIP-02.
+
+pub mod advertisement;
+pub mod gate;
+pub mod meter;
+pub mod pricing;
+pub mod session;