scripts/taler-landing: full-scan bank collector with GOA alt units

Add a host-side Python collector that lists every bank account, pages
through all ledger rows, and emits stats.json with amount_alt fields
(Kilo/Mega/Peta-GOA) so large ladder withdrawals fit on the landing tiles.

scripts/taler-landing/enrich_stats_alt.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+"""Add amount_alt / amount_full fields to a landing stats.json in place."""
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent))
+from goa_amounts import DEFAULT_ALT, enrich_stats_tree, load_alt_from_config  # noqa: E402
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser()
+    ap.add_argument("path", help="stats.json path")
+    ap.add_argument(
+        "--exchange-config",
+        default="https://exchange.hacktivism.ch/config",
+    )
+    ap.add_argument("-o", "--out", default="", help="default: overwrite path")
+    args = ap.parse_args()
+    p = Path(args.path)
+    data = json.loads(p.read_text(encoding="utf-8"))
+    if not isinstance(data, dict) or not data.get("ok"):
+        print("skip: not ok stats", file=sys.stderr)
+        return 0
+    alt = load_alt_from_config(args.exchange_config) or dict(DEFAULT_ALT)
+    enrich_stats_tree(data, alt)
+    out = Path(args.out) if args.out else p
+    tmp = out.with_suffix(out.suffix + f".tmp.{os.getpid()}")
+    tmp.write_text(json.dumps(data, indent=2, ensure_ascii=False) + "\n", encoding="utf-8")
+    tmp.replace(out)
+    print(f"enriched {out}", file=sys.stderr)
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())