fix(logging): let debug: true reach stderr, not only the log file

[bakiburakogun]

Fixes #347

Problem

logger_config.yaml pins the stderr handler at WARNING, so with debug: true the detail goes to persistent_storage/logs/ccb.log while docker logs stays nearly silent. logger_config.k8s.yaml already has stderr at DEBUG, so only the manual-install and Docker paths are affected.

Everything describing what indexing is doing is INFO or DEBUG — Dispatching N file chunk(s), Waiting for file chunk 1/8 future to complete, embed_sources finished for 4 source(s): 3 succeeded, 1 errored with its per-source error dict. None of it surfaces. What does surface is the occasional ERROR traceback with no context around it, so from outside the container a healthy-but-slow run and a stuck one look identical.

Change

When debug is on, lower the stderr handler along with the logger levels. Reading the app config a few lines earlier is what makes it possible to decide before dictConfig runs. The default stays WARNING, so nothing changes for anyone who has not asked for debug; the file handler is untouched.

Guarded with .get() so a config without a stderr handler — a custom one, say — still starts.

Testing

On a four-node deployment with debug: true: before the change docker logs showed only startup lines and error tracebacks; after it, the batch dispatch and per-source results appear, which is what made diagnosing #345 possible without going into the container to read ccb.log.