feat(understand): room frames, the nearest panel and possible packages — what the field test asked for

The takeoffs were run again on a real P&ID pair (kept outside the repository)
and compared with the hand-made workbooks. The user chose how three gaps
should close:

- Rooms drawn as frames. A room label that no wall face holds takes the
  smallest closed, straight-sided polyline around it, provided it holds no
  other room number and is at least ten label heights a side (label+frame,
  0.8). A P&ID draws its rooms this way, so P&ID lengths are now cut at the
  frames rather than sent to the nearest label. An unnumbered mention inside
  a frame ('hot room') does not deny it.
- The nearest panel, flagged. cable_takeoff(panel_rule="nearest") is the
  default: a load that no callout places takes the nearest panel on the
  layout, among names with a panel prefix (is_panel_name: CP, JB, DB,
  MCC ...) or names a callout gives. The row is flagged panel_inferred, and
  an inferred panel never makes a package. panel_rule="stated" keeps the old
  behaviour. The takeoff_roundtrip gate and the cable correctness check read
  stated panels only: a guess is no evidence.
- Possible packages and detail copies. pipe_takeoff reports detail_copies:
  compact groups of tags drawn twice (repeated), and compact groups of one
  equipment's own parts, such as M150B, M150C and M150D of M150 (family). A
  vendor package or an equipment detail shows up this way. Nothing is
  removed until exclude_regions names a region. The runs left out go to the
  control rows as excluded_region and to excluded_m. The workbook's method
  sheet names the regions.

Each change has a synthetic test that failed first. Suite: 4986 passed, 1
xfailed. The inventory and the document numbers match (README: 4987
collected).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

tests/test_understand_labels.py

@@ -11,6 +11,7 @@ import pytest
 
 from engineering.understand.labels import (
     CYRILLIC_LOOKALIKES,
+    is_panel_name,
     normalize_panel,
     parse_diameters,
     parse_electrical,
@@ -212,6 +213,15 @@ def test_wiring_callouts_in_four_languages():
     assert wiring_target("CP 2 panosuna") == "CP-2"
 
 
+def test_a_panel_name_is_told_by_its_letters():
+    # normalize_panel reads any letters-and-digits token; only a panel prefix
+    # (control panel, junction box, distribution board, MCC ...) makes a panel
+    assert is_panel_name("CP-1") and is_panel_name("JB-2") and is_panel_name("CP-M82")
+    assert is_panel_name("MCC-3") and is_panel_name("DB-12")
+    assert not is_panel_name("M-87") and not is_panel_name("T-4100")
+    assert not is_panel_name(None) and not is_panel_name("")
+
+
 def test_the_russian_to_before_a_panel_is_a_wiring_callout():
     # A Russian P&ID closes a load's text with the panel it is wired to: 'к CP1'
     # ('to CP1'), or 'к щиту CP-2' ('to switchboard CP-2'). The unit кВт holds