fix: Logger default WARNING→INFO + structured PeerTube logging

Log level: production default was Level::Warning, but all facades
(AppLogger, AdminLogger, Audit) write at Monolog INFO level. This
silently discarded submission, admin action, and audit logs when
LOG_LEVEL env var was unset. Changed to Level::Info.

PeerTube: replaced raw error_log() calls in PeerTubeService::upload(),
deleteVideo(), FilepondHandler::process(), ThesisCreateController,
and ThesisFileHandler with structured logging:
- Successes → Logger::get('app')->info() (visible in App — soumissions tab)
- Failures  → ErrorHandler::log('peertube_*', ...) (visible in Erreurs tab)
Added require_once for Logger and ErrorHandler in PeerTubeService.

TODO.md

@@ -51,3 +51,5 @@
 - [x] Fix repertoire Années column: sort reverse chronological (newest first) instead of ascending alpha
 - [x] TFE website embed: wrap iframe + button in overlay-style div with "Site web" pill badge on left corner, clearer link text
 - [x] Redirect internal metadata links on TFE page from /repertoire to /search (orientation, AP, finalité, year, keywords); add query= for search bar prefill; fix filter <details> visibility on desktop; add keyword to filterKeys badge; add hidden keyword input + visible chip to filter form so keyword filter survives form submission
+- [x] Fix Logger default level: production default was WARNING, but all facades (AppLogger, AdminLogger, Audit) write at INFO — causing submission/admin/audit logs to be silently discarded
+- [x] Add structured logging to PeerTube upload/delete: replace raw error_log() with Logger::get('app')->info() for successes and ErrorHandler::log() for failures in PeerTubeService, FilepondHandler, ThesisCreateController, ThesisFileHandler