feat(compliance): USBM RI8507/OSMRE compliance chart + reference doc

sfm/compliance.py renders the velocity-vs-frequency blasting compliance chart
Blastware draws on its Event Report:
- limit_at()/limit_curve() — the RI8507 Fig B-1 / 30 CFR 816.67 curve as data
  (Drywall 0.75 + plaster 0.50 lines): 0.030in low-freq bound, plateau, 0.008in
  rising diagonal to a 2.0 in/s cap at ~40 Hz, drawn continuous.
- channel_compliance_points() — the per-cycle (freq, peak-velocity) scatter by
  the zero-crossing method (matches Blastware; cloud ceiling = channel PPV).
- draw_compliance_chart() — matplotlib rendering (both lines + scatter, BW tick
  scales + channel markers).

Verified against 7 BE12844 Blastware reports. docs/ri8507_compliance_curve.md
captures the curve construction, the SHM basis, and the scatter method.

Not yet wired into report_pdf.py — that placeholder is the next step.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YDXjZCr4RqT2U3QvMDhgzf

tests/test_compliance.py

@@ -0,0 +1,35 @@
+"""USBM/OSMRE compliance curve + scatter logic (sfm.compliance).
+Rendering is verified visually against Blastware reports."""
+import math
+
+import numpy as np
+
+from sfm.compliance import limit_at, channel_compliance_points
+
+
+def test_osmre_velocity_segments():
+    assert abs(limit_at(6.0) - 0.75) < 1e-9      # 3.5–12 Hz flat
+    assert abs(limit_at(50.0) - 2.00) < 1e-9     # 30–100 Hz flat
+
+
+def test_displacement_segments():
+    assert abs(limit_at(2.0) - 2 * math.pi * 2.0 * 0.030) < 1e-9    # low-freq 0.030 in
+    assert abs(limit_at(20.0) - 2 * math.pi * 20.0 * 0.008) < 1e-9  # rising diagonal 0.008 in
+
+
+def test_limit_clamps_below_1hz():
+    assert limit_at(0.1) == limit_at(1.0)
+
+
+def test_scatter_ceiling_is_ppv_at_dominant_freq():
+    # ~27 Hz blast-like trace whose energy peaks mid-record (inside full cycles,
+    # as a real event does): the scatter cloud's ceiling is the trace PPV and the
+    # top point sits near the dominant frequency.
+    sps, n = 1024.0, 3328
+    t = np.arange(n) / sps
+    env = np.exp(-((t - 1.5) ** 2) / (2 * 0.3 ** 2))
+    x = 0.9 * env * np.sin(2 * np.pi * 27.0 * t)
+    f, v = channel_compliance_points(x, sps)
+    assert len(f) > 20
+    assert v.max() >= 0.99 * np.abs(x).max()
+    assert 20.0 < f[int(np.argmax(v))] < 35.0