feat(understand): the snapshot, the vocabulary and the label parsers; MAX_DXF_BYTES 512 MB; the office extra

Track H's foundation, landed on main before its three groups branch.

- engineering/understand/snapshot.py: one bulk read of a drawing into frozen
  WCS records (OCS translated through backends/ocs.py, text decoded, an
  INSERT boxed by its block geometry without its attribute texts). A DXF is
  read with ezdxf after the size check; the headless engine's document is
  read under its own lock; the live engine exports the active document with
  Document.Export(<tmp>/snap, "DXF", <set of all>) - never renamed, deleted
  afterwards - and a DWG is opened read-only, exported and closed. Measured on
  AutoCAD 2026: ".dxf" is refused with Invalid argument, the file lands as
  snap.DXF, model space, paper space and unused block definitions all reach
  it, and the selection set does not narrow a DXF export.
- engineering/understand/labels.py: %%c, \U+2205, the U+2300 sign, o-stroke
  and MTEXT format runs all read as one diameter spelling; sizes are kept as
  drawn and never equated; Cyrillic look-alike capitals fold into Latin tags;
  panels, wiring callouts and electrical data (kW, phases, volts, N, VFD) in
  EN / TR / RU / NL / DE. A power that is not written stays None.
- engineering/understand/vocab.py: layer classification with a confidence and
  the deciding keyword, supply / return words, room labels and block kinds in
  five languages. A CIP layer without a direction word is not guessed.
- MAX_DXF_BYTES defaults to 512 MB (a real layout was 188 MB); the refusal
  names the size and the variable. New `office` extra (openpyxl), also in
  `full`; uv.lock regenerated.

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

config.py

@@ -9,6 +9,9 @@ from pathlib import Path
 #: CAD this project is developed and tested against.
 DEFAULT_CAD_PROGID = "AutoCAD.Application"
 
+#: Default ``MAX_DXF_BYTES``: 512 MB.
+DEFAULT_MAX_DXF_BYTES = 512 * 1024 * 1024
+
 
 class Settings:
     """Server configuration loaded from environment variables."""
@@ -62,9 +65,12 @@ class Settings:
             os.environ.get("DANGEROUS_COMMANDS_ENABLED", "false").lower().strip() == "true"
         )
 
-        # Reject opening DXF files larger than this many bytes (default 50 MB).
-        # Set to 0 to disable the check.
-        self.max_dxf_bytes: int = int(os.environ.get("MAX_DXF_BYTES", str(50 * 1024 * 1024)))
+        # Reject opening DXF files larger than this many bytes (default 512 MB).
+        # Set to 0 to disable the check. It was 50 MB until v1.6's track H: a
+        # real plant layout read on 2026-09-24 was a 188 MB DXF, and the
+        # understanding tools exist for exactly such drawings. The refusal
+        # names the file's size and this variable.
+        self.max_dxf_bytes: int = int(os.environ.get("MAX_DXF_BYTES", str(DEFAULT_MAX_DXF_BYTES)))
 
         # Hard cap on list/select limit params to keep tool responses bounded.
         self.max_list_limit: int = int(os.environ.get("MAX_LIST_LIMIT", "5000"))