Fix: CsI(Tl) non-linear response correction + detector calibration overhaul

Root cause of Am-241 misidentification: the Radiacode 103's CsI(Tl) crystal
shifts low-energy peaks upward (59.5 keV → 71.6 keV for Am-241) due to
non-proportional scintillation response. The model was trained on theoretical
peak positions and couldn't match the shifted real peaks.

Changes:
- Add inverse CsI(Tl) non-linear correction to inference pipeline
  (radiacode_monitor.py, web/config.py, test_detection.py)
  E_apparent = E_true * (1 + 0.37 * exp(-E_true/100))
  Corrects channel mapping so peaks appear at theoretical energies
- Fix energy calibration: DetectorConfig now uses E = 0.33 + 2.97*ch
  with 1023 channels, matching the real detector (was energy_min=20,
  skip_first_channel=True, different channel width)
- Add K-escape peaks for CsI(Tl) iodine X-ray escape (E - 28.5 keV)
- Add asymmetric peak shapes for low-energy tails (< 200 keV)
- Add log1p normalization in dataset and inference (replaces max-norm)
- Add background-subtracted training mode (subtract_background flag)
- Add low-signal augmentation (0.01-5 Bq activities, 30-300s durations)
- Update docker-compose.yml: batch_size=32, duration=30-300s,
  CSI_NONLINEAR_ALPHA/BETA env vars for detect and web
- Web dashboard: apply CsI correction to displayed spectra
- Various UI fixes (Chart.js width, zoom/pan, isotope lines)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/app/theoretical_bg.py

@@ -30,7 +30,7 @@ def generate_continuum_only(cps: float = 6.0, live_time_s: float = 3600.0):
     energy_axis = ENERGY_OFFSET + ENERGY_SLOPE * channels
     total_counts = cps * live_time_s
 
-    # Try calibrated spline first
+    # Try calibrated spline first (fits measured background)
     continuum_cps = _get_continuum_cps()
 
     if continuum_cps is not None and len(continuum_cps) == NUM_CHANNELS:
@@ -39,7 +39,7 @@ def generate_continuum_only(cps: float = 6.0, live_time_s: float = 3600.0):
         if continuum.sum() > 0:
             continuum *= total_counts / continuum.sum()
     else:
-        # Fallback: simple parametric model
+        # Fallback: parametric model
         continuum = _fallback_continuum(energy_axis, total_counts)
 
     return {