Fix mode panels: Screen → Container with on_show/on_hide lifecycle

Textual's ContentSwitcher expects regular Widget/Container children,
not Screen subclasses. Screen's on_mount fires for all children at
once regardless of visibility, so demo workers for all 5 modes
started simultaneously and competed for the bridge.

Container children get proper on_show/on_hide from ContentSwitcher's
visibility toggling — only the active panel's worker runs.

tui/src/skywalker_tui/screens/lband.py

@@ -10,8 +10,7 @@ import os
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "tools"))
 
 from textual.app import ComposeResult
-from textual.containers import Horizontal, Vertical
+from textual.containers import Container, Horizontal, Vertical
-from textual.screen import Screen
 from textual.widgets import Label, Input, Button, Static, ProgressBar, Checkbox
 from textual import work
 from textual.worker import Worker
@@ -37,7 +36,7 @@ def _alloc_table(start: float, stop: float) -> str:
     return "\n".join(lines)
 
 
-class LBandScreen(Screen):
+class LBandScreen(Container):
     """L-band direct input analyzer with allocation annotations."""
 
     DEFAULT_CSS = """
@@ -130,11 +129,11 @@ class LBandScreen(Screen):
             yield Button("Sweep", id="lband-sweep-btn", variant="success")
             yield Button("Stop", id="lband-stop-btn", variant="error")
 
-    def on_mount(self) -> None:
+    def on_show(self) -> None:
-        if self._bridge.is_demo:
+        if self._bridge.is_demo and not self._sweeping:
             self._start_sweep()
 
-    def on_unmount(self) -> None:
+    def on_hide(self) -> None:
         self._stop_sweep()
 
     def on_button_pressed(self, event: Button.Pressed) -> None:

tui/src/skywalker_tui/screens/monitor.py

@@ -6,8 +6,7 @@ sparkline history.
 """
 
 from textual.app import ComposeResult
-from textual.containers import Horizontal, Vertical
+from textual.containers import Container, Horizontal, Vertical
-from textual.screen import Screen
 from textual.widgets import Label, Input, Button, Static
 from textual import work
 from textual.worker import Worker, WorkerState
@@ -16,7 +15,7 @@ from skywalker_tui.widgets.signal_gauge import SignalGauge
 from skywalker_tui.widgets.sparkline_widget import SparklineWidget
 
 
-class MonitorScreen(Screen):
+class MonitorScreen(Container):
     """Real-time signal monitor with gauge and sparkline."""
 
     DEFAULT_CSS = """
@@ -96,12 +95,12 @@ class MonitorScreen(Screen):
             yield Button("Start", id="mon-start", variant="success")
             yield Button("Stop", id="mon-stop", variant="error")
 
-    def on_mount(self) -> None:
+    def on_show(self) -> None:
         # Auto-start polling in demo mode
-        if self._bridge.is_demo:
+        if self._bridge.is_demo and not self._polling:
             self._start_polling()
 
-    def on_unmount(self) -> None:
+    def on_hide(self) -> None:
         self._stop_polling()
 
     def on_button_pressed(self, event: Button.Pressed) -> None:

tui/src/skywalker_tui/screens/scan.py

@@ -8,8 +8,7 @@ import struct
 import time
 
 from textual.app import ComposeResult
-from textual.containers import Horizontal, Vertical
+from textual.containers import Container, Horizontal, Vertical
-from textual.screen import Screen
 from textual.widgets import Label, Input, Button, Static, ProgressBar
 from textual import work
 from textual.worker import Worker
@@ -18,7 +17,7 @@ from skywalker_tui.widgets.spectrum_plot import SpectrumPlot
 from skywalker_tui.widgets.frequency_table import FrequencyTable
 
 
-class ScanScreen(Screen):
+class ScanScreen(Container):
     """Multi-phase transponder scanner with progress and results table."""
 
     DEFAULT_CSS = """
@@ -111,7 +110,7 @@ class ScanScreen(Screen):
             yield Button("Scan", id="scan-start-btn", variant="success")
             yield Button("Stop", id="scan-stop-btn", variant="error")
 
-    def on_unmount(self) -> None:
+    def on_hide(self) -> None:
         self._stop_scan()
 
     def on_button_pressed(self, event: Button.Pressed) -> None:

tui/src/skywalker_tui/screens/spectrum.py

@@ -5,8 +5,7 @@ waterfall beneath it. Uses threaded workers for the blocking USB sweep.
 """
 
 from textual.app import ComposeResult
-from textual.containers import Horizontal, Vertical
+from textual.containers import Container, Horizontal, Vertical
-from textual.screen import Screen
 from textual.widgets import Label, Input, Button, Static, ProgressBar, Checkbox
 from textual import work
 from textual.worker import Worker
@@ -15,7 +14,7 @@ from skywalker_tui.widgets.spectrum_plot import SpectrumPlot
 from skywalker_tui.widgets.waterfall import WaterfallDisplay
 
 
-class SpectrumScreen(Screen):
+class SpectrumScreen(Container):
     """Spectrum analyzer with bar chart and optional waterfall."""
 
     DEFAULT_CSS = """
@@ -94,11 +93,11 @@ class SpectrumScreen(Screen):
             yield Button("Sweep", id="spec-sweep-btn", variant="success")
             yield Button("Stop", id="spec-stop-btn", variant="error")
 
-    def on_mount(self) -> None:
+    def on_show(self) -> None:
-        if self._bridge.is_demo:
+        if self._bridge.is_demo and not self._sweeping:
             self._start_sweep()
 
-    def on_unmount(self) -> None:
+    def on_hide(self) -> None:
         self._stop_sweep()
 
     def on_button_pressed(self, event: Button.Pressed) -> None:

tui/src/skywalker_tui/screens/track.py

@@ -12,8 +12,7 @@ from datetime import datetime
 from pathlib import Path
 
 from textual.app import ComposeResult
-from textual.containers import Horizontal, Vertical
+from textual.containers import Container, Horizontal, Vertical
-from textual.screen import Screen
 from textual.widgets import Label, Input, Button, Static, RichLog
 from textual import work
 from textual.worker import Worker
@@ -22,7 +21,7 @@ from skywalker_tui.widgets.signal_gauge import SignalGauge
 from skywalker_tui.widgets.sparkline_widget import SparklineWidget
 
 
-class TrackScreen(Screen):
+class TrackScreen(Container):
     """Long-running carrier tracker with event log and export."""
 
     DEFAULT_CSS = """
@@ -137,11 +136,11 @@ class TrackScreen(Screen):
             yield Button("Export CSV", id="trk-csv-btn")
             yield Button("Export JSONL", id="trk-jsonl-btn")
 
-    def on_mount(self) -> None:
+    def on_show(self) -> None:
-        if self._bridge.is_demo:
+        if self._bridge.is_demo and not self._tracking:
             self._start_tracking()
 
-    def on_unmount(self) -> None:
+    def on_hide(self) -> None:
         self._stop_tracking()
 
     def on_button_pressed(self, event: Button.Pressed) -> None: