Phase 2: extract headless core modules (sras_format, scan_geometry, config)

- core/sras_format.py: THE v6 implementation — create_scan_file (writer,
  byte-identical to the old one, enforced against the Phase-0 goldens),
  SrasFile parser with frontier/truncation walk, and zero-copy mmap
  load_angle/load_row views for multi-GB files
- core/scan_geometry.py: ScanPlan/AngleGeometry dataclasses, build_plan
  (rotated-bbox trig from MainWindow._build_scan_params), travel-limit
  validate_plan (limits now a StageLimits dataclass, not literals buried
  in the worker), format_eta + EtaEstimator (bounded deque)
- core/config.py: ScanDefaults dataclass replaces the module-import-time
  dict globals. FIXES: editing any main-window port used to rewrite
  aui_defaults.json without helios_port, silently reverting the Helios
  port every time (test_helios_port_survives_partial_update covers it).
  Also drops the inert laser_freq_hz plumbing — scans always used the
  LASER_FREQ_HZ constant.
- hardware/serial_util.py: shared 8N1 open + scored port enumeration
  (promoted from t3r_control_panel); helios_laser and the panel use it
- sc3_aui_app.py and sras_scan_manager.py migrated onto core (three
  format implementations down to one); ScanWorker now takes a ScanPlan
- tests: byte-identical writer vs golden, frontier over every truncation
  variant, mmap==eager, geometry vs golden fixtures + invariants, config
  round-trip. 28 passing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

t3r_control_panel.py

@@ -28,8 +28,8 @@ from PyQt6.QtWidgets import (
 )
 
 from hardware.t3r_driver import T3RDriver
+from hardware.serial_util import scored_ports
 import hardware.t3r_protocol as proto
-import serial.tools.list_ports
 
 
 # ── Utilities ─────────────────────────────────────────────────────────────────
@@ -613,16 +613,8 @@ class T3RControlPanel(QDialog):
     def _refresh_ports(self):
         current = self.port_combo.currentText()
         self.port_combo.clear()
-        ports = list(serial.tools.list_ports.comports())
-
-        def score(p):
-            text = f"{p.description} {p.manufacturer or ''} {p.product or ''}".lower()
-            hints = ("esp32", "jtag", "espressif", "usb serial", "cp210", "ch340", "cdc")
-            return -sum(h in text for h in hints)
-
-        ports.sort(key=score)
-        for p in ports:
-            self.port_combo.addItem(f"{p.device} — {p.description or p.device}", p.device)
+        for device, label in scored_ports():
+            self.port_combo.addItem(label, device)
         if self.port_combo.count() == 0:
             self.port_combo.addItem("(no serial ports found)", None)
         elif current: