feat(tscm): add custom frequency range option to RF sweep

Adds a "Custom Range" sweep type that lets users specify start/end MHz
instead of using a fixed preset. Useful in dense RF environments where
a full or standard sweep returns too many signals and causes slowdown.

UI shows start/end MHz inputs when "Custom Range" is selected. Range is
validated (0 < start < end ≤ 6000 MHz) before the sweep starts.
Backend threads the ranges through to _scan_rf_signals(), which already
supports arbitrary frequency bands.

Closes #172

routes/tscm/__init__.py

@@ -490,6 +490,7 @@ def _start_sweep_internal(
     bt_interface: str = '',
     sdr_device: int | None = None,
     verbose_results: bool = False,
+    custom_ranges: list[dict] | None = None,
 ) -> dict:
     """Start a TSCM sweep without request context."""
     global _sweep_running, _sweep_thread, _current_sweep_id
@@ -532,7 +533,7 @@ def _start_sweep_internal(
     _sweep_thread = threading.Thread(
         target=_run_sweep,
         args=(sweep_type, baseline_id, wifi_enabled, bt_enabled, rf_enabled,
-              wifi_interface, bt_interface, sdr_device, verbose_results),
+              wifi_interface, bt_interface, sdr_device, verbose_results, custom_ranges),
         daemon=True
     )
     _sweep_thread.start()
@@ -1127,7 +1128,8 @@ def _run_sweep(
     wifi_interface: str = '',
     bt_interface: str = '',
     sdr_device: int | None = None,
-    verbose_results: bool = False
+    verbose_results: bool = False,
+    custom_ranges: list[dict] | None = None,
 ) -> None:
     """
     Run the TSCM sweep in a background thread.
@@ -1504,7 +1506,7 @@ def _run_sweep(
                         'rf_count': len(all_rf),
                     })
                     # Try RF scan even if sdr_device is None (will use device 0)
-                    rf_signals = _scan_rf_signals(sdr_device, sweep_ranges=preset.get('ranges'))
+                    rf_signals = _scan_rf_signals(sdr_device, sweep_ranges=custom_ranges or preset.get('ranges'))
 
                     # If no signals and this is first RF scan, send info event
                     if not rf_signals and last_rf_scan == 0:

routes/tscm/sweep.py

@@ -58,6 +58,25 @@ def start_sweep():
     bt_interface = data.get('bt_interface', '')
     sdr_device = data.get('sdr_device')
 
+    # Validate custom frequency ranges if provided
+    custom_ranges = None
+    if sweep_type == 'custom':
+        raw_ranges = data.get('custom_ranges') or []
+        validated = []
+        for rng in raw_ranges:
+            try:
+                start = float(rng.get('start', 0))
+                end = float(rng.get('end', 0))
+                step = float(rng.get('step', 0.1))
+                if 0 < start < end <= 6000:
+                    validated.append({'start': start, 'end': end, 'step': step,
+                                      'name': rng.get('name') or f'{start:.0f}–{end:.0f} MHz'})
+            except (TypeError, ValueError):
+                pass
+        if not validated:
+            return jsonify({'status': 'error', 'message': 'custom sweep requires valid start/end MHz'}), 400
+        custom_ranges = validated
+
     result = _start_sweep_internal(
         sweep_type=sweep_type,
         baseline_id=baseline_id,
@@ -68,6 +87,7 @@ def start_sweep():
         bt_interface=bt_interface,
         sdr_device=sdr_device,
         verbose_results=verbose_results,
+        custom_ranges=custom_ranges,
     )
     http_status = result.pop('http_status', 200)
     return jsonify(result), http_status