feat(pusher): add opt-in v2 WeTime ping signing

- Add WELIST_PING_SIG_VERSION (1 legacy, 2 canonical JSON); default 1
- Sign WELIST-PING-V2\n + compact sorted JSON covering url, chain, height,
  median_time, last_block_hash, info, base_fee, version and sig_version
- Fetch info/base_fee/version from the local /{chain}/info endpoint and sign them
- Fall back to null metadata on fetch failure; skip the fetch for onion URLs
- Normalize the advertised URL and bound metadata to match the WeTime service
- Activate v2 in bal-pusher.sh and document the TXT record setup
- Add unit tests for canonical payloads, URL normalization, metadata and onion detection

Includes previously uncommitted local deployment hardening:
- pg-server.sh configurable loopback bind address, volume and recreate handling
- .env loading in bal-server.sh and bal-pusher.sh
- second bal-server/bal-pusher development scripts

README.md

@@ -148,6 +148,7 @@ If no network is specified, defaults to `bitcoin`.
 | `BAL_SERVER_URL` | URL of bal-server (for stats reporting). | - |
 | `SSL_KEY_PATH` | Ed25519 private key for signing stats reports. | `private_key.pem` |
 | `WELIST_SERVER_URL` | Welist server URL. | `https://welist.bitcoin-after.life` |
+| `WELIST_PING_SIG_VERSION` | WeTime ping signature scheme (`1` legacy, `2` canonical JSON). | `1` |
 
 ### Per-network configuration