feat: Add currency management feature with CRUD operations

- Introduced a new template for currency overview and management (`currencies.html`).
- Updated footer to include attribution to AllYouCanGET.
- Added "Currencies" link to the main navigation header.
- Implemented end-to-end tests for currency creation, update, and activation toggling.
- Created unit tests for currency API endpoints, including creation, updating, and activation toggling.
- Added a fixture to seed default currencies for testing.
- Enhanced database setup tests to ensure proper seeding and migration handling.

docs/logging_audit.md

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+# Setup Script Logging Audit (2025-10-25)
+
+The following observations capture current logging behaviour in `scripts/setup_database.py` and highlight areas requiring improved error handling and messaging.
+
+## Connection Validation
+
+- `validate_admin_connection` and `validate_application_connection` log entry/exit messages and raise `RuntimeError` with context if connection fails. This coverage is sufficient.
+- `ensure_database` logs creation states but does not surface connection or SQL exceptions beyond the initial connection acquisition. When the inner `cursor.execute` calls fail, the exceptions bubble without contextual logging.
+
+## Migration Runner
+
+- Lists pending migrations and logs each application attempt.
+- When the baseline is pending, the script logs whether it is a dry-run or live application and records legacy file marking. However, if `_apply_migration_file` raises an exception, the caller re-raises after logging the failure; there is no wrapping message guiding users toward manual cleanup.
+- Legacy migration marking happens silently (just info logs). Failures during the insert into `schema_migrations` would currently propagate without added guidance.
+
+## Seeding Workflow
+
+- `seed_baseline_data` announces each seeding phase and skips verification in dry-run mode with a log breadcrumb.
+- `_verify_seeded_data` warns about missing currencies/units and inactive defaults but does **not** raise errors, meaning CI can pass while the database is incomplete. There is no explicit log when verification succeeds.
+- `_seed_units` logs when the `measurement_unit` table is missing, which is helpful, but the warning is the only feedback; no exception is raised.
+
+## Suggested Enhancements
+
+1. Wrap baseline application and legacy marking in `try/except` blocks that log actionable remediation steps before re-raising.
+2. Promote seed verification failures (missing or inactive records) to exceptions so automated workflows fail fast; add success logs for clarity.
+3. Add contextual logging around currency/measurement-unit insert failures, particularly around `execute_values` calls, to aid debugging malformed data.
+4. Introduce structured logging (log codes or phases) for major steps (`CONNECT`, `MIGRATE`, `SEED`, `VERIFY`) to make scanning log files easier.
+
+These findings inform the remaining TODO subtasks for enhanced error handling.