add Iroh P2P transport alongside TCP listener

[rueckwaerts]

Adds Iroh QUIC-based P2P transport as an alternative to TCP/Tor.

What this does

• Adds src/iroh_listener.rs — Iroh endpoint running parallel to TCP
• Persistent secret key stored in /data/iroh_secret_key.bin
• Node ID written to /data/iroh_node_id.txt on startup
• ALPN protocol: electrs/electrum/0
• Graceful handling of invalid/empty key files (regenerates instead of panic)

How to connect

Server address in Electrum: <NODE_ID>:1:i

Tested on

• StartOS 0.4.0-beta.9 (x86_64)
• Electrum 4.7.2 with custom Iroh transport (rueckwaerts/electrum)
• End-to-end: wallet sync, transaction history, real-time updates

Notes

• Uses iroh 0.35.0 (Python bindings available)
• Upgrade to iroh 1.x planned when Python bindings are released
• Runs parallel to existing TCP listener — no breaking changes