…nd readiness endpoints

- Introduce `HealthcheckLogFilter` to omit unnecessary healthcheck logs.
- Apply filter to `uvicorn.access` logger during logging configuration.

- Changed logging statements in `active_pastes_counter.py` from `info` to `debug` for better verbosity control.
- Explicitly set root logger level during configuration to enforce uniform logging levels.
- Unified uvicorn logger formatting and applied consistent configuration for text and JSON formats.
- Integrated healthcheck log filter into uvicorn access logger setup.

…backend

…ing-and-open-lang-supp

feat: add syntax highlighting to fe and arbitrary lang support to be