fix: correctness, cross-backend parity & enforced quality gate (audit Sprints 2-4)

Audit-driven fixes across the dual backend, the premium workflow, and the
engineering layer. 318 tests, ruff-clean.

Quality gate (the moat):
- drawing_finalize now runs the premium ISO-128 critique in addition to the
  8-step validator; leftover construction, non-ISO lineweights, untrimmed
  corners, duplicates and dim overlap block the gate (strict_critique fails on
  warnings too).
- dim_overlap critique no longer a no-op (dim reference point + bbox fallback);
  dim/construction layers resolve from the active layer set (iso13567 too).

Stability / correctness:
- view_screenshot & drawing_export_pdf render headless via Agg (no more
  worker-thread SIGSEGV).
- gear tooth profile no longer self-overlaps at high tooth counts; section view
  no longer duplicates bore lines; validator keyway heuristic fixed.
- ezdxf aligned/angular dim API, full-circle polar array duplicate already
  covered by Sprint 1; this bundle adds save-format-from-extension,
  entity_offset side selection, ARC length, properties parity (bounding_box /
  rotation / char_height), mtext rotation.

COM robustness (mocked-COM tested):
- CoUninitialize on teardown; transaction commit/rollback try/finally + UNDO via
  the CMDACTIVE guard; system_run_lisp guard + USERS1 value capture;
  set_variable type coercion; HWND via Application.HWND; BlockInfo.description.

Security:
- HTTP remote-bind guard fires on every launch path (incl. `fastmcp run`);
  StaticTokenVerifier wired into FastMCP; AutoLISP allowlist bypass-vector tests.

Hygiene: linetype-on-demand in _apply_attrs, honest view_zoom returns, snap-on-arc
sweep handling, point_tangent acos clamp, dynamic tool_groups / tool count,
word-boundary SPUR/HELICAL, undo-stack locking.

Deferred: R22 (undo/transaction stack isolation) lands with the I1 refiner (1.2),
which depends on it.

tests/test_com_backend.py

@@ -39,6 +39,10 @@ NL_TABLE: list[tuple[Any, Any]] = [
     (50, 50),
     (100, 100),
     (200, 200),
+    # Ambiguous bare ints (<= 2.05) — the P0 truncation hazard: treated as mm,
+    # NOT as hundredths (NEW-test-com-1). 2 -> 2.00mm -> 200, 1 -> 1.00mm -> 100.
+    (1, 100),
+    (2, 200),
     # Sentinels: -1 = ByLayer, -2 = ByBlock, -3 = Default
     (-1, -1),
     (-2, -2),