Add DemoCraftClient for complete offline demo mode

- DemoCraftClient in demo.py: duck-typed CraftClient replacement with
  8 canned satellites, synthetic pass predictions, and time-varying LEO
  arcs that drive real AOS/TCA/LOS pass events to the camera overlay
- Fix sky map EL signal fidelity: snap _el to _target_el at sweep start
  so 2D scans compute correct per-row RSSI (was using stale elevation)
- Branch on demo_mode in app.py _setup_craft_client() to inject
  DemoCraftClient instead of the HTTP CraftClient
- Add test_demo_craft.py: 5 tests exercising search, passes, tracking,
  and WAITING state through the full TUI without mocks
- Update take_screenshots.py to cover all 8 screens (dashboard, control,
  craft search, craft tracking, signal, system, console, camera)

tui/tests/test_demo_craft.py

@@ -0,0 +1,164 @@
+"""Test DemoCraftClient — full Craft lifecycle in demo mode.
+
+Unlike test_craft_mode.py which uses MagicMock, these tests run with the
+real DemoCraftClient to verify the end-to-end demo experience: search,
+pass predictions, and tracking with time-varying satellite positions.
+
+No network calls are made.
+"""
+
+import asyncio
+
+import pytest
+
+from birdcage_tui.app import BirdcageApp
+from birdcage_tui.screens.control import ControlScreen
+from birdcage_tui.widgets.craft_panel import CraftPanel, CraftTrackingStatus
+
+
+async def _switch_to_craft(pilot, app) -> None:
+    """Navigate to F2 Control > Craft sub-mode."""
+    await pilot.press("f2")
+    await pilot.pause()
+    control = app.query_one("#control", ControlScreen)
+    control.switch_mode("craft")
+    await pilot.pause()
+
+
+@pytest.mark.asyncio
+async def test_demo_search_returns_results():
+    """DemoCraftClient search should populate the DataTable."""
+    app = BirdcageApp()
+    app.demo_mode = True
+
+    async with app.run_test(size=(120, 40)) as pilot:
+        await pilot.pause()
+        await _switch_to_craft(pilot, app)
+
+        panel = app.query_one("#ctrl-craft-panel", CraftPanel)
+        panel.post_message(CraftPanel.SearchRequested("ISS"))
+        await asyncio.sleep(0.5)
+
+        from textual.widgets import DataTable
+
+        table = app.query_one("#craft-results-table", DataTable)
+        assert table.row_count >= 1
+        first_key = list(table.rows.keys())[0]
+        row = table.get_row(first_key)
+        assert "ISS" in row[0]
+
+
+@pytest.mark.asyncio
+async def test_demo_broad_search():
+    """Empty query should return the full demo catalog."""
+    app = BirdcageApp()
+    app.demo_mode = True
+
+    async with app.run_test(size=(120, 40)) as pilot:
+        await pilot.pause()
+        await _switch_to_craft(pilot, app)
+
+        panel = app.query_one("#ctrl-craft-panel", CraftPanel)
+        panel.post_message(CraftPanel.SearchRequested(""))
+        await asyncio.sleep(0.5)
+
+        from textual.widgets import DataTable
+
+        table = app.query_one("#craft-results-table", DataTable)
+        assert table.row_count == 8  # Full demo catalog
+
+
+@pytest.mark.asyncio
+async def test_demo_passes():
+    """DemoCraftClient should return synthetic pass predictions."""
+    app = BirdcageApp()
+    app.demo_mode = True
+
+    async with app.run_test(size=(120, 40)) as pilot:
+        await pilot.pause()
+        await _switch_to_craft(pilot, app)
+
+        control = app.query_one("#control", ControlScreen)
+        panel = app.query_one("#ctrl-craft-panel", CraftPanel)
+
+        panel.post_message(CraftPanel.PassesRequested(norad_id=25544))
+        await asyncio.sleep(0.5)
+
+        from birdcage_tui.widgets.craft_panel import CraftPassInfo
+
+        info = app.query_one("#craft-pass-info", CraftPassInfo)
+        # Should contain max elevation of 55.0 degrees (ISS arc)
+        assert "55.0" in info.passes_text
+
+
+@pytest.mark.asyncio
+async def test_demo_tracking_drives_device():
+    """DemoCraftClient tracking should move the demo device."""
+    app = BirdcageApp()
+    app.demo_mode = True
+
+    async with app.run_test(size=(120, 40)) as pilot:
+        await pilot.pause()
+        await _switch_to_craft(pilot, app)
+
+        panel = app.query_one("#ctrl-craft-panel", CraftPanel)
+
+        # Track the Moon — always above horizon in demo
+        panel.post_message(
+            CraftPanel.TrackRequested(
+                target_type="celestial",
+                target_id="moon",
+                name="Moon",
+                min_el=5.0,
+            )
+        )
+        await asyncio.sleep(2.5)
+
+        status = app.query_one("#craft-tracking-status", CraftTrackingStatus)
+        assert status.state == "TRACKING"
+        assert status.moves >= 1
+
+        # Device should have been commanded toward the Moon's position
+        assert app.device._target_az > 100.0  # Moon is around AZ 145
+        assert app.device._target_el > 20.0   # Moon is around EL 32
+
+        # Screenshot for visual verification
+        app.save_screenshot("/tmp/birdcage_demo_craft_tracking.svg")
+
+        # Stop tracking
+        control = app.query_one("#control", ControlScreen)
+        control._stop_craft_tracking()
+        await pilot.pause()
+
+
+@pytest.mark.asyncio
+async def test_demo_tracking_waiting_below_horizon():
+    """Tracking a below-horizon LEO target shows WAITING."""
+    app = BirdcageApp()
+    app.demo_mode = True
+
+    async with app.run_test(size=(120, 40)) as pilot:
+        await pilot.pause()
+        await _switch_to_craft(pilot, app)
+
+        panel = app.query_one("#ctrl-craft-panel", CraftPanel)
+
+        # SO-50 may be below horizon depending on timing.
+        # Use Jupiter at min_el=90 to guarantee WAITING.
+        panel.post_message(
+            CraftPanel.TrackRequested(
+                target_type="celestial",
+                target_id="jupiter",
+                name="Jupiter",
+                min_el=90.0,  # Impossible — forces WAITING
+            )
+        )
+        await asyncio.sleep(2.0)
+
+        status = app.query_one("#craft-tracking-status", CraftTrackingStatus)
+        assert status.state == "WAITING"
+
+        # Cleanup
+        control = app.query_one("#control", ControlScreen)
+        control._stop_craft_tracking()
+        await pilot.pause()