Add Camera Capture overlay (F6) with multi-trigger capture pipeline

Camera backend abstraction wrapping fswebcam/ffmpeg/libcamera-still via
subprocess, with DemoCamera fallback generating valid JPEG from raw bytes.

Capture pipeline writes JPEG + JSON sidecar always, optional FITS (astropy)
and EXIF (Pillow) when available. Thread-safe orchestrator with session
tracking, sequence numbering, and date-based output directories.

Trigger system: manual capture, configurable interval timer, and pass event
detection (AOS/TCA/LOS) with 0.5-degree TCA hysteresis. PassEventDetector
runs in the Craft tracking loop, fires callbacks to the camera overlay.

F6 overlay follows the F5 ConsoleOverlay pattern — ModalScreen with
install_screen persistence. Status panel, scrollable capture log, interval
controls, and AOS/TCA/LOS toggle buttons.

Tagline: "a generic AZ/EL positioner that doesn't care about wavelength"
added to TUI header subtitle.

51 new tests (77 total passing).

tui/tests/test_capture_manager.py

@@ -0,0 +1,171 @@
+"""Test capture manager — file naming, JSON sidecars, session tracking.
+
+All tests use DemoCamera for zero-hardware-dependency captures.
+"""
+
+import json
+from pathlib import Path
+
+import pytest
+
+from birdcage_tui.camera import DemoCamera
+from birdcage_tui.capture_manager import (
+    CaptureManager,
+    CaptureMetadata,
+    CaptureSession,
+    _build_filename,
+    _sanitize_name,
+)
+
+
+@pytest.fixture
+def manager(tmp_path: Path) -> CaptureManager:
+    """CaptureManager with DemoCamera in a temp directory."""
+    backend = DemoCamera()
+    return CaptureManager(backend, output_dir=tmp_path)
+
+
+@pytest.fixture
+def tracking_metadata() -> CaptureMetadata:
+    """Metadata simulating an active tracking capture."""
+    return CaptureMetadata(
+        mount_az=245.30,
+        mount_el=34.20,
+        target_name="ISS (ZARYA)",
+        target_type="satellite",
+        target_id="25544",
+        target_az=245.30,
+        target_el=34.20,
+        target_distance_km=420.0,
+        target_range_rate=-2.1,
+        tracking_mode="craft",
+        tracking_status="TRACKING",
+        trigger="manual",
+    )
+
+
+def test_capture_writes_jpeg(manager: CaptureManager, tracking_metadata):
+    """Capture should produce a JPEG file."""
+    result = manager.capture(tracking_metadata)
+    assert result.success
+    assert result.path.exists()
+    assert result.path.suffix == ".jpg"
+
+
+def test_capture_writes_json_sidecar(manager: CaptureManager, tracking_metadata):
+    """JSON sidecar should always be written alongside JPEG."""
+    result = manager.capture(tracking_metadata)
+    assert result.success
+
+    # Find the JSON sidecar
+    json_files = list(result.path.parent.glob("*.json"))
+    assert len(json_files) == 1
+
+    data = json.loads(json_files[0].read_text())
+    assert data["mount_az"] == 245.30
+    assert data["mount_el"] == 34.20
+    assert data["target_name"] == "ISS (ZARYA)"
+    assert data["trigger"] == "manual"
+
+
+def test_filename_generation():
+    """Filenames should follow the naming convention."""
+    meta = CaptureMetadata(
+        mount_az=245.30,
+        mount_el=34.20,
+        target_name="ISS (ZARYA)",
+        timestamp="2026-02-16T08:25:00Z",
+    )
+    name = _build_filename(meta, "jpg")
+    assert name.startswith("ISS-ZARYA_")
+    assert "245.30" in name
+    assert "34.20" in name
+    assert name.endswith(".jpg")
+
+
+def test_filename_sanitization():
+    """Special characters should be stripped from target names."""
+    assert _sanitize_name("ISS (ZARYA)") == "ISS-ZARYA"
+    assert _sanitize_name("NOAA 19") == "NOAA-19"
+    assert _sanitize_name("") == "manual"
+    assert _sanitize_name("a/b\\c:d") == "abcd"
+
+
+def test_filename_no_target():
+    """Without a target name, filename should use 'manual'."""
+    meta = CaptureMetadata(
+        mount_az=180.0,
+        mount_el=45.0,
+        timestamp="2026-02-16T12:00:00Z",
+    )
+    name = _build_filename(meta, "jpg")
+    assert name.startswith("manual_")
+
+
+def test_session_counter():
+    """Session sequence should increment monotonically."""
+    session = CaptureSession()
+    assert session.next_sequence() == 1
+    assert session.next_sequence() == 2
+    assert session.next_sequence() == 3
+    assert session.capture_count == 3
+
+
+def test_session_id_unique():
+    """Each session should have a unique ID."""
+    s1 = CaptureSession()
+    s2 = CaptureSession()
+    assert s1.session_id != s2.session_id
+
+
+def test_subdirectory_creation(manager: CaptureManager, tracking_metadata):
+    """Captures should go into date-based subdirectories."""
+    result = manager.capture(tracking_metadata)
+    assert result.success
+    # The parent should be a date directory like "2026-02-16"
+    parent = result.path.parent.name
+    assert len(parent) == 10  # YYYY-MM-DD
+    assert parent.count("-") == 2
+
+
+def test_multiple_captures_increment(manager: CaptureManager, tracking_metadata):
+    """Multiple captures should increment the session counter."""
+    r1 = manager.capture(tracking_metadata)
+    r2 = manager.capture(tracking_metadata)
+    assert r1.success and r2.success
+    assert manager.session.capture_count == 2
+    # Filenames should differ
+    assert r1.path.name != r2.path.name
+
+
+def test_pillow_fallback(manager: CaptureManager):
+    """Manager should report Pillow status without crashing."""
+    # This test just verifies the property doesn't throw
+    _ = manager.has_pillow  # True if installed, False if not
+
+
+def test_astropy_fallback(manager: CaptureManager):
+    """Manager should report astropy status without crashing."""
+    _ = manager.has_astropy  # True if installed, False if not
+
+
+def test_metadata_session_populated(manager: CaptureManager, tracking_metadata):
+    """After capture, metadata should have session info populated."""
+    manager.capture(tracking_metadata)
+    assert tracking_metadata.session_id == manager.session.session_id
+    assert tracking_metadata.sequence_number == 1
+
+
+def test_manual_capture_no_target(manager: CaptureManager):
+    """Capture without tracking should work with minimal metadata."""
+    meta = CaptureMetadata(
+        mount_az=180.0,
+        mount_el=45.0,
+        trigger="manual",
+    )
+    result = manager.capture(meta)
+    assert result.success
+
+    # JSON sidecar should exist
+    json_files = list(result.path.parent.glob("*.json"))
+    assert len(json_files) >= 1