Added a new `.coveragerc` file configuring coverage thresholds and exclusions.
Included `pytest.ini` to enable coverage reporting for multiple backend modules (`main`, `llm`, `prompt`, `geoip`, `tts_asr`) with a 90 % fail‑under requirement and detailed HTML output.
Implemented a suite of unit tests:
* `test_geoip.py` – validates geo‑location lookup logic.
* `test_llm_extended.py` – tests LLm response extraction and Ollama interactions.
* `test_main_endpoints.py` – covers API endpoints for completions, OCR, and TTS.
* `test_prompt_extended.py` – verifies language sanitization, timestamp generation, and prompt building.
* `test_tts_asr_coverage.py` – checks device detection, cache clearing, and model loading under various environment configurations.
* `test_tts_asr_extended.py` – further tests TTS/ASR device selection and time‑outs.
Updated `backend/requirements.txt` to use newer, compatible packages, removed obsolete testing dependencies, and added `qwen-tts`.
Modified `backend/tts_asr.py` to work with the new `Qwen3TTSModel`, simplified imports, and adjusted device mapping logic.
Additionally, frontend changes added a new `TreeNodeItem` component, updated Markdown rendering, added TTS instruction fields, and reworked context menu handling.
No breaking changes were introduced.
