feat: CI pipeline, lint fixes, and Renovate config

- pyproject.toml with ruff/pytest config (setuptools<81 pin)
- Full test suite (26 tests)
- Gitea Actions CI (lint, test, docker, notify)
- Ruff lint/format fixes across source files
- Renovate config for automated dependency updates

Ref: ADR-0057

tests/conftest.py

@@ -0,0 +1,71 @@
+"""
+Pytest configuration and fixtures for stt-module tests.
+"""
+
+import asyncio
+import base64
+import os
+import struct
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+# Set test environment variables before importing
+os.environ.setdefault("NATS_URL", "nats://localhost:4222")
+os.environ.setdefault("WHISPER_URL", "http://localhost:8000")
+os.environ.setdefault("OTEL_ENABLED", "false")
+os.environ.setdefault("STT_ENABLE_VAD", "false")
+
+
+@pytest.fixture(scope="session")
+def event_loop():
+    """Create event loop for async tests."""
+    loop = asyncio.new_event_loop()
+    yield loop
+    loop.close()
+
+
+@pytest.fixture
+def silent_pcm_bytes():
+    """16-bit PCM silence (1000 samples at 16kHz = 62.5ms)."""
+    return bytes([0x00] * 2000)
+
+
+@pytest.fixture
+def noisy_pcm_bytes():
+    """16-bit PCM with some signal (sine-like pattern)."""
+    samples = []
+    for i in range(1000):
+        val = int(16000 * ((i % 50) / 50.0 - 0.5))
+        samples.append(struct.pack("<h", val))
+    return b"".join(samples)
+
+
+@pytest.fixture
+def sample_audio_b64(silent_pcm_bytes):
+    """Base64-encoded silent PCM audio."""
+    return base64.b64encode(silent_pcm_bytes).decode()
+
+
+@pytest.fixture
+def mock_nats():
+    """Mock NATS connection."""
+    nc = AsyncMock()
+    nc.publish = AsyncMock()
+    nc.subscribe = AsyncMock()
+    nc.close = AsyncMock()
+    nc.jetstream = MagicMock(return_value=AsyncMock())
+    return nc
+
+
+@pytest.fixture
+def mock_http_client():
+    """Mock httpx async client."""
+    client = AsyncMock()
+    response = MagicMock()
+    response.status_code = 200
+    response.json.return_value = {"text": "Hello world"}
+    response.raise_for_status = MagicMock()
+    client.post = AsyncMock(return_value=response)
+    client.aclose = AsyncMock()
+    return client