Add bank maintenance script to raise all account debit limits.

mytops-style dry-run tool; PATCH debit_threshold for every libeufin account.

scripts/taler-bank/maintenance/README.md

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+# taler-bank maintenance
+
+One-shot ops tools for **libeufin-bank** on koopa (`taler-hacktivism-bank`).  
+Pattern matches **mytops-admin-log** `scripts/taler-merchant/maintenance/`: **dry-run by default**, `--no-dry` to apply.
+
+## `raise-debit-limits.sh`
+
+Raise **`debit_threshold`** on every bank account (overdraft / withdraw headroom).  
+Optionally set **`DEFAULT_DEBT_LIMIT`** for new accounts.
+
+| | |
+|--|--|
+| **Default amount** | `GOA:4503599627370496` (libeufin amount ceiling ≈ 2⁵²) |
+| **Auth** | admin password: `BANK_ADMIN_PASS` or `bank-admin-password.txt` |
+| **Bank** | `http://127.0.0.1:9012` on koopa, or `podman exec` into `taler-hacktivism-bank` |
+
+### Usage
+
+```bash
+# on koopa (hernani), after bank is up:
+cd ~/path/to/koopa-admin-log   # or copy script
+
+# preview
+./scripts/taler-bank/maintenance/raise-debit-limits.sh
+
+# apply to all accounts
+./scripts/taler-bank/maintenance/raise-debit-limits.sh --no-dry
+
+# apply + DEFAULT_DEBT_LIMIT in container overrides + bank restart
+./scripts/taler-bank/maintenance/raise-debit-limits.sh --no-dry --set-default
+
+# custom amount / single user
+./scripts/taler-bank/maintenance/raise-debit-limits.sh --no-dry --amount GOA:1000000 --only explorer
+```
+
+Via container if host cannot reach :9012:
+
+```bash
+podman exec -u root -i taler-hacktivism-bank bash -s -- --no-dry \
+  < scripts/taler-bank/maintenance/raise-debit-limits.sh
+```
+
+### Notes
+
+- Does **not** invent balance; only raises how far accounts may go into **debit**.
+- Exchange coin denominations (largest `GOA:1000`) are separate — large withdraws still work with many coins.
+- Secrets never live in this repo — see `SECRETS.md` / `koopa-admin-secrets`.