test(backend): add comprehensive test coverage for backend modules

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.

backend/tests/test_geoip.py

@@ -0,0 +1,168 @@
+import sys
+import os
+import types
+import pathlib
+import pytest
+
+# Ensure the backend directory is on sys.path so we can import the geoip module directly
+BACKEND_DIR = pathlib.Path(__file__).resolve().parents[1]  # backend/ folder
+if str(BACKEND_DIR) not in sys.path:
+    sys.path.insert(0, str(BACKEND_DIR))
+
+import geoip as geoip
+
+
+@pytest.fixture(autouse=True)
+def reset_geoip_reader():
+    # Ensure each test starts with a clean cache
+    geoip._geoip_reader = None
+    yield
+    geoip._geoip_reader = None
+
+
+def test_get_reader_import_error(monkeypatch):
+    import builtins
+    real_import = getattr(builtins, "__import__")
+
+    def fake_import(name, globals=None, locals=None, fromlist=(), level=0):
+        if name == "geoip2.database":
+            raise ImportError("simulate missing geoip2")
+        return real_import(name, globals, locals, fromlist, level)
+
+    monkeypatch.setattr(builtins, "__import__", fake_import)
+
+    geoip._geoip_reader = None
+    assert geoip._get_reader() is None
+
+
+def test_get_reader_db_missing(monkeypatch):
+    # Provide a fake geoip2 module, but force the database file to be considered missing
+    fake_db_module = types.ModuleType("geoip2.database")
+    class FakeReader:
+        def __init__(self, path):
+            self.path = path
+    fake_db_module.Reader = FakeReader
+
+    fake_geoip2 = types.ModuleType("geoip2")
+    fake_geoip2.database = fake_db_module
+
+    sys.modules["geoip2"] = fake_geoip2
+    sys.modules["geoip2.database"] = fake_db_module
+
+    # Ensure path existence check returns False
+    monkeypatch.setattr(geoip.os.path, "exists", lambda p: False)
+
+    geoip._geoip_reader = None
+    assert geoip._get_reader() is None
+
+    # Clean up injected modules
+    del sys.modules["geoip2"]
+    del sys.modules["geoip2.database"]
+
+
+def test_get_reader_loads_and_caches(monkeypatch):
+    fake_db_module = types.ModuleType("geoip2.database")
+    class FakeReader:
+        def __init__(self, path):
+            self.path = path
+    fake_db_module.Reader = FakeReader
+
+    fake_geoip2 = types.ModuleType("geoip2")
+    fake_geoip2.database = fake_db_module
+
+    sys.modules["geoip2"] = fake_geoip2
+    sys.modules["geoip2.database"] = fake_db_module
+
+    # Simulate that the database file exists
+    monkeypatch.setattr(geoip.os.path, "exists", lambda p: True)
+
+    geoip._geoip_reader = None
+    r1 = geoip._get_reader()
+    assert isinstance(r1, FakeReader)
+    # Second call should return the same cached instance
+    r2 = geoip._get_reader()
+    assert r1 is r2
+    # Clean up injected modules
+    del sys.modules["geoip2"]
+    del sys.modules["geoip2.database"]
+
+
+@pytest.mark.parametrize("ip", [None, "", "127.0.0.1", "localhost", "::1"])
+def test_get_ip_location_none_inputs(ip):
+    assert geoip.get_ip_location(ip) is None
+
+
+def test_get_ip_location_reader_none(monkeypatch):
+    # When there is no reader (no database), return None
+    monkeypatch.setattr(geoip, "_get_reader", lambda: None)
+    assert geoip.get_ip_location("1.2.3.4") is None
+
+
+def test_get_ip_location_successful_lookup(monkeypatch):
+    from types import SimpleNamespace
+
+    country = SimpleNamespace(name="United States")
+    region = SimpleNamespace(name="California")
+    resp = SimpleNamespace(
+        country=country,
+        subdivisions=SimpleNamespace(most_specific=region),
+        city=SimpleNamespace(name="Mountain View"),
+    )
+
+    class FakeReader:
+        def city(self, ip):
+            return resp
+
+    monkeypatch.setattr(geoip, "_get_reader", lambda: FakeReader())
+    loc = geoip.get_ip_location("1.2.3.4")
+    assert loc == {
+        "country": "United States",
+        "region": "California",
+        "city": "Mountain View",
+        "display": "United States California Mountain View",
+    }
+
+
+def test_get_ip_location_reader_exception(monkeypatch):
+    class FakeReader:
+        def city(self, ip):
+            raise Exception("boom")
+
+    monkeypatch.setattr(geoip, "_get_reader", lambda: FakeReader())
+    assert geoip.get_ip_location("1.2.3.4") is None
+
+
+def test_get_ip_location_no_location_parts(monkeypatch):
+    from types import SimpleNamespace
+    resp = SimpleNamespace(country=SimpleNamespace(name=None), subdivisions=None, city=None)
+
+    class FakeReader:
+        def city(self, ip):
+            return resp
+
+    monkeypatch.setattr(geoip, "_get_reader", lambda: FakeReader())
+    assert geoip.get_ip_location("1.2.3.4") is None
+
+
+def test_get_ip_location_text_valid(monkeypatch):
+    from types import SimpleNamespace
+    country = SimpleNamespace(name="United States")
+    region = SimpleNamespace(name="California")
+    resp = SimpleNamespace(
+        country=country,
+        subdivisions=SimpleNamespace(most_specific=region),
+        city=SimpleNamespace(name="Mountain View"),
+    )
+
+    class FakeReader:
+        def city(self, ip):
+            return resp
+
+    monkeypatch.setattr(geoip, "_get_reader", lambda: FakeReader())
+    assert geoip.get_ip_location_text("1.2.3.4") == "United States California Mountain View"
+
+
+def test_get_ip_location_text_none_when_no_location(monkeypatch):
+    # Force get_ip_location to return None
+    monkeypatch.setattr(geoip, "get_ip_location", lambda ip: None)
+    assert geoip.get_ip_location_text("1.2.3.4") == ""