refactor: phase 1 - testability improvements

- Add Config dataclass with get_config()/set_config() for injection
- Add Config.from_args() for CLI argument parsing (testable)
- Add platform font path detection (Darwin/Linux)
- Bound translate cache with @lru_cache(maxsize=500)
- Add fixtures for external dependencies (network, feeds, config)
- Add 15 tests for Config class, from_args, and platform detection

This enables testability by:
- Allowing config injection instead of global mutable state
- Supporting custom argv in from_args() for testing
- Providing reusable fixtures for mocking network/filesystem
- Preventing unbounded memory growth in translation cache

Fixes: _arg_value/_arg_int not accepting custom argv

tests/fixtures/__init__.py

@@ -0,0 +1,236 @@
+"""
+Pytest fixtures for mocking external dependencies (network, filesystem).
+"""
+
+import json
+from unittest.mock import MagicMock
+
+import pytest
+
+
+@pytest.fixture
+def mock_feed_response():
+    """Mock RSS feed response data."""
+    return b"""<?xml version="1.0" encoding="UTF-8" ?>
+<rss version="2.0">
+  <channel>
+    <title>Test Feed</title>
+    <link>https://example.com</link>
+    <item>
+      <title>Test Headline One</title>
+      <pubDate>Sat, 15 Mar 2025 12:00:00 GMT</pubDate>
+    </item>
+    <item>
+      <title>Test Headline Two</title>
+      <pubDate>Sat, 15 Mar 2025 11:00:00 GMT</pubDate>
+    </item>
+    <item>
+      <title>Sports: Team Wins Championship</title>
+      <pubDate>Sat, 15 Mar 2025 10:00:00 GMT</pubDate>
+    </item>
+  </channel>
+</rss>"""
+
+
+@pytest.fixture
+def mock_gutenberg_response():
+    """Mock Project Gutenberg text response."""
+    return """Project Gutenberg's Collection, by Various
+
+*** START OF SOME TEXT ***
+This is a test poem with multiple lines
+that should be parsed as stanzas.
+
+Another stanza here with different content
+and more lines to test the parsing logic.
+
+Yet another stanza for variety
+in the test data.
+
+*** END OF SOME TEXT ***"""
+
+
+@pytest.fixture
+def mock_gutenberg_empty():
+    """Mock Gutenberg response with no valid stanzas."""
+    return """Project Gutenberg's Collection
+
+*** START OF TEXT ***
+THIS IS ALL CAPS AND SHOULD BE SKIPPED
+
+I.
+
+*** END OF TEXT ***"""
+
+
+@pytest.fixture
+def mock_ntfy_message():
+    """Mock ntfy.sh SSE message."""
+    return json.dumps(
+        {
+            "id": "test123",
+            "event": "message",
+            "title": "Test Title",
+            "message": "Test message body",
+            "time": 1234567890,
+        }
+    ).encode()
+
+
+@pytest.fixture
+def mock_ntfy_keepalive():
+    """Mock ntfy.sh keepalive message."""
+    return b'data: {"event":"keepalive"}\n\n'
+
+
+@pytest.fixture
+def mock_google_translate_response():
+    """Mock Google Translate API response."""
+    return json.dumps(
+        [
+            [["Translated text", "Original text", None, 0.8], None, "en"],
+            None,
+            None,
+            [],
+            [],
+            [],
+            [],
+        ]
+    )
+
+
+@pytest.fixture
+def mock_feedparser():
+    """Create a mock feedparser.parse function."""
+
+    def _mock(data):
+        mock_result = MagicMock()
+        mock_result.bozo = False
+        mock_result.entries = [
+            {
+                "title": "Test Headline",
+                "published_parsed": (2025, 3, 15, 12, 0, 0, 0, 0, 0),
+            },
+            {
+                "title": "Another Headline",
+                "updated_parsed": (2025, 3, 15, 11, 0, 0, 0, 0, 0),
+            },
+        ]
+        return mock_result
+
+    return _mock
+
+
+@pytest.fixture
+def mock_urllib_open(mock_feed_response):
+    """Create a mock urllib.request.urlopen that returns feed data."""
+
+    def _mock(url):
+        mock_response = MagicMock()
+        mock_response.read.return_value = mock_feed_response
+        return mock_response
+
+    return _mock
+
+
+@pytest.fixture
+def sample_items():
+    """Sample items as returned by fetch module (title, source, timestamp)."""
+    return [
+        ("Headline One", "Test Source", "12:00"),
+        ("Headline Two", "Another Source", "11:30"),
+        ("Headline Three", "Third Source", "10:45"),
+    ]
+
+
+@pytest.fixture
+def sample_config():
+    """Sample config for testing."""
+    from engine.config import Config
+
+    return Config(
+        headline_limit=100,
+        feed_timeout=10,
+        mic_threshold_db=50,
+        mode="news",
+        firehose=False,
+        ntfy_topic="https://ntfy.sh/test/json",
+        ntfy_reconnect_delay=5,
+        message_display_secs=30,
+        font_dir="fonts",
+        font_path="",
+        font_index=0,
+        font_picker=False,
+        font_sz=60,
+        render_h=8,
+        ssaa=4,
+        scroll_dur=5.625,
+        frame_dt=0.05,
+        firehose_h=12,
+        grad_speed=0.08,
+        glitch_glyphs="░▒▓█▌▐",
+        kata_glyphs="ﾊﾐﾋｰｳ",
+        script_fonts={},
+    )
+
+
+@pytest.fixture
+def poetry_config():
+    """Sample config for poetry mode."""
+    from engine.config import Config
+
+    return Config(
+        headline_limit=100,
+        feed_timeout=10,
+        mic_threshold_db=50,
+        mode="poetry",
+        firehose=False,
+        ntfy_topic="https://ntfy.sh/test/json",
+        ntfy_reconnect_delay=5,
+        message_display_secs=30,
+        font_dir="fonts",
+        font_path="",
+        font_index=0,
+        font_picker=False,
+        font_sz=60,
+        render_h=8,
+        ssaa=4,
+        scroll_dur=5.625,
+        frame_dt=0.05,
+        firehose_h=12,
+        grad_speed=0.08,
+        glitch_glyphs="░▒▓█▌▐",
+        kata_glyphs="ﾊﾐﾋｰｳ",
+        script_fonts={},
+    )
+
+
+@pytest.fixture
+def firehose_config():
+    """Sample config with firehose enabled."""
+    from engine.config import Config
+
+    return Config(
+        headline_limit=100,
+        feed_timeout=10,
+        mic_threshold_db=50,
+        mode="news",
+        firehose=True,
+        ntfy_topic="https://ntfy.sh/test/json",
+        ntfy_reconnect_delay=5,
+        message_display_secs=30,
+        font_dir="fonts",
+        font_path="",
+        font_index=0,
+        font_picker=False,
+        font_sz=60,
+        render_h=8,
+        ssaa=4,
+        scroll_dur=5.625,
+        frame_dt=0.05,
+        firehose_h=12,
+        grad_speed=0.08,
+        glitch_glyphs="░▒▓█▌▐",
+        kata_glyphs="ﾊﾐﾋｰｳ",
+        script_fonts={},
+    )