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/src/birdcage_tui/app.py

@@ -16,6 +16,7 @@ from textual.binding import Binding
 from textual.containers import Horizontal
 from textual.widgets import Button, ContentSwitcher, Footer, Header
 
+from birdcage_tui.screens.camera import CameraOverlay
 from birdcage_tui.screens.console import ConsoleOverlay
 from birdcage_tui.screens.control import ControlScreen
 from birdcage_tui.screens.dashboard import DashboardScreen
@@ -45,6 +46,7 @@ class BirdcageApp(App):
         Binding("f3", "switch_tab('signal')", "Signal"),
         Binding("f4", "switch_tab('system')", "System"),
         Binding("f5", "toggle_console", "Console"),
+        Binding("f6", "toggle_camera", "Camera"),
         Binding("q", "quit", "Quit"),
         Binding("d", "toggle_dark", "Dark"),
     ]
@@ -55,6 +57,8 @@ class BirdcageApp(App):
     firmware_name: str = "g2"
     skip_init: bool = False
     craft_url: str = "https://space.warehack.ing"
+    capture_dir: str = "captures"
+    camera_device: str = "auto"
     device: object = None
     shutdown_event: threading.Event = threading.Event()
 
@@ -64,12 +68,15 @@ class BirdcageApp(App):
     _prev_az: float = 0.0
     _prev_el: float = 0.0
     _console_visible: bool = False
+    _camera_visible: bool = False
+    _pass_detector: object = None  # PassEventDetector, set by CameraOverlay
 
     @property
     def SUB_TITLE(self) -> str:  # noqa: N802
+        tag = "a generic AZ/EL positioner that doesn't care about wavelength"
         if self.demo_mode:
-            return "DEMO"
-        return self.serial_port
+            return f"{tag}  ·  DEMO"
+        return f"{tag}  ·  {self.serial_port}"
 
     def compose(self) -> ComposeResult:
         yield Header()
@@ -114,6 +121,7 @@ class BirdcageApp(App):
         self._setup_craft_client()
         self._update_status_strip_connection()
         self._install_console()
+        self._install_camera()
         self._start_position_poll()
 
     async def _initialize_device(self) -> None:
@@ -159,6 +167,10 @@ class BirdcageApp(App):
         """Pre-install the console overlay so it persists across open/close."""
         self.install_screen(ConsoleOverlay(), name="console-overlay")
 
+    def _install_camera(self) -> None:
+        """Pre-install the camera overlay so it persists across open/close."""
+        self.install_screen(CameraOverlay(), name="camera-overlay")
+
     # ------------------------------------------------------------------
     # App-level position poll
     # ------------------------------------------------------------------
@@ -246,6 +258,25 @@ class BirdcageApp(App):
         """Called when the console overlay is dismissed."""
         self._console_visible = False
 
+    # ------------------------------------------------------------------
+    # Camera overlay
+    # ------------------------------------------------------------------
+
+    def action_toggle_camera(self) -> None:
+        """Push or pop the camera capture overlay."""
+        if self._camera_visible:
+            try:
+                self.pop_screen()
+            except Exception:
+                self._camera_visible = False
+        else:
+            self.push_screen("camera-overlay", callback=self._on_camera_dismissed)
+            self._camera_visible = True
+
+    def _on_camera_dismissed(self, _result=None) -> None:
+        """Called when the camera overlay is dismissed."""
+        self._camera_visible = False
+
     # ------------------------------------------------------------------
     # Tab bar button handling
     # ------------------------------------------------------------------
@@ -329,6 +360,16 @@ def main() -> None:
         default="https://space.warehack.ing",
         help="Craft API base URL",
     )
+    parser.add_argument(
+        "--capture-dir",
+        default="captures",
+        help="Output directory for camera captures",
+    )
+    parser.add_argument(
+        "--camera-device",
+        default="auto",
+        help="Camera device (e.g., /dev/video0) or 'auto'",
+    )
     args = parser.parse_args()
 
     app = BirdcageApp()
@@ -337,6 +378,8 @@ def main() -> None:
     app.firmware_name = args.firmware
     app.skip_init = args.skip_init
     app.craft_url = args.craft_url
+    app.capture_dir = args.capture_dir
+    app.camera_device = args.camera_device
     try:
         app.run()
     except KeyboardInterrupt: