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-server.sh

@@ -4,6 +4,14 @@ 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=$(pwd)
 if [ ! -f "$WORKING_DIR/public_key.pem" ]; then
   echo_i "creating keypairs"