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

bal-pusher-2.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Second bal-pusher instance: talks to the second bal-server and database.
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+. "$SCRIPT_DIR/lib.sh"
+
+# Load local, gitignored environment overrides (e.g. BAL_PG_PASSWORD).
+if [ -f "$SCRIPT_DIR/.env" ]; then
+    set -a
+    # shellcheck disable=SC1091
+    . "$SCRIPT_DIR/.env"
+    set +a
+fi
+
+WORKING_DIR=$(pwd)
+
+export RUST_LOG=trace
+
+export BAL_SERVER_DB_FILE="$WORKING_DIR/bal2.db"
+export BAL_SERVER_DB_BACKEND="postgresql"
+#export BAL_PUSHER_BITCOIN_COOKIE_FILE=/~/.bitcoin/.cookie
+#export BAL_PUSHER_REGTEST_COOKIE_FILE=/~/.bitcoin/regtest/.cookie
+#export BAL_PUSHER_TESTNET_COOKIE_FILE=/~/.bitcoin/testnet3/.cookie
+#export BAL_PUSHER_SIGNET_COOKIE_FILE=/~/.bitcoin/signet/.cookie
+
+export BAL_PUSHER_REGTEST_ZMQ_HASHBLOCK=tcp://127.0.0.1:21332
+# Only the first pusher reports executor stats, to avoid double reporting for
+# the same executor key on the welist service.
+export BAL_PUSHER_SEND_STATS=false
+export WELIST_SERVER_URL=http://localhost:8086
+export WELIST_SKIP_URL_VALIDATION=true
+export BAL_SERVER_URL="http://127.0.0.1:9134"
+export SSL_KEY_PATH="$WORKING_DIR/private_key.pem"
+
+# Instance-specific settings must win over .env, which defines BAL_PG_DB=baldb.
+export BAL_PG_DB="baldb2"
+unset BAL_SERVER_PG_DSN
+
+if [ "$BAL_SERVER_DB_BACKEND" = "postgresql" ]; then
+    . "$SCRIPT_DIR/pg-server.sh"
+fi
+
+cargo run --bin=bal-pusher regtest --features=pusher