Configurable logging system + exception/content logging fixes

[damienlaine]

Why

Logging was 5 scattered basicConfig() calls, plain text on stdout only, with a single DEBUG toggle. No way to ship logs to a centralized system. This makes logging configurable like the LinTO Studio API (Winston): selectable sinks, text or JSON, per-sink levels.

Commit 1 — feature: configurable logging

• Central app/core/logging_config.py (setup_logging), called once per process (API, Celery, seeds), replacing the scattered basicConfig calls.
• Driven by env vars (LOG_LEVEL, LOG_FORMAT text|json, LOG_NAME, per-sink levels) or a full dictConfig JSON file via LOGGING_CONFIG_FILE (Winston WINSTON_CONFIG_PATH equivalent).
• Sinks: console, rotating file, non-blocking HTTP POST (background queue), Google Cloud Logging / Stackdriver (optional dep).
• JSON logs: ISO-8601 timestamps with millisecond precision, service label per process, extra={...} fields preserved.
• uvicorn access logs flow through the same sinks (log_config=None), /healthcheck still filtered.
• Adds python-json-logger, docs/LOGGING_GUIDE.md, and tests/test_logging_config.py (19 tests).

Commit 2 — fix: exception & content logging quality

• Tracebacks: 71 except handlers logged only the exception string. Converted logger.error -> logger.exception and added exc_info=True to warning/critical inside except blocks. logger.exception count 1 -> 83, exc_info=True 0 -> 16.
• Privacy: stopped dumping LLM responses, extracted document content and prompt bodies in logs (kept lengths, field names and ids). Notably the JIT-extraction INFO log no longer logs document content.

Verification

• AST check: every logger.exception / exc_info=True sits inside an active except (no "NoneType: None").
• Only logging lines changed in the reviewed files — no control-flow/behavior changes.
• py_compile OK on all changed files; 775 tests collect with no import errors; 186 passed / 0 failed on the subset touching the changed modules.

Notes

• google-cloud-logging is left commented in requirements.txt (optional, lazy-imported); uncomment to enable the Stackdriver sink.
• Default behavior is unchanged: text logs on stdout. Set LOG_FORMAT=json for aggregators.