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

uv.lock

@@ -82,9 +82,13 @@ com = [
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 full = [
     { name = "matplotlib" },
+    { name = "openpyxl" },
     { name = "pillow" },
     { name = "pywin32", marker = "sys_platform == 'win32'" },
 ]
+office = [
+    { name = "openpyxl" },
+]
 pdf = [
     { name = "matplotlib" },
 ]
@@ -103,13 +107,15 @@ requires-dist = [
     { name = "fastmcp", specifier = ">=3.4.5,<4" },
     { name = "matplotlib", marker = "extra == 'full'", specifier = ">=3.8" },
     { name = "matplotlib", marker = "extra == 'pdf'", specifier = ">=3.8" },
+    { name = "openpyxl", marker = "extra == 'full'", specifier = ">=3.1" },
+    { name = "openpyxl", marker = "extra == 'office'", specifier = ">=3.1" },
     { name = "pillow", marker = "extra == 'com'", specifier = ">=10.0" },
     { name = "pillow", marker = "extra == 'full'", specifier = ">=10.0" },
     { name = "pydantic", specifier = ">=2.0,<3" },
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     { name = "pywin32", marker = "sys_platform == 'win32' and extra == 'full'", specifier = ">=306" },
 ]
-provides-extras = ["com", "pdf", "full"]
+provides-extras = ["com", "pdf", "office", "full"]
 
 [package.metadata.requires-dev]
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+[[package]]
+name = "et-xmlfile"
+version = "2.0.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/d3/38/af70d7ab1ae9d4da450eeec1fa3918940a5fafb9055e934af8d6eb0c2313/et_xmlfile-2.0.0.tar.gz", hash = "sha256:dab3f4764309081ce75662649be815c4c9081e88f0837825f90fd28317d4da54", size = 17234, upload-time = "2024-10-25T17:25:40.039Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/c1/8b/5fe2cc11fee489817272089c4203e679c63b570a5aaeb18d852ae3cbba6a/et_xmlfile-2.0.0-py3-none-any.whl", hash = "sha256:7a91720bc756843502c3b7504c77b8fe44217c85c537d85037f0f536151b2caa", size = 18059, upload-time = "2024-10-25T17:25:39.051Z" },
+]
+
 [[package]]
 name = "exceptiongroup"
 version = "1.3.1"
@@ -1344,6 +1359,18 @@ wheels = [
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+[[package]]
+name = "openpyxl"
+version = "3.1.5"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "et-xmlfile" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/3d/f9/88d94a75de065ea32619465d2f77b29a0469500e99012523b91cc4141cd1/openpyxl-3.1.5.tar.gz", hash = "sha256:cf0e3cf56142039133628b5acffe8ef0c12bc902d2aadd3e0fe5878dc08d1050", size = 186464, upload-time = "2024-06-28T14:03:44.161Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/c0/da/977ded879c29cbd04de313843e76868e6e13408a94ed6b987245dc7c8506/openpyxl-3.1.5-py2.py3-none-any.whl", hash = "sha256:5282c12b107bffeef825f4617dc029afaf41d0ea60823bbb665ef3079dc79de2", size = 250910, upload-time = "2024-06-28T14:03:41.161Z" },
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 [[package]]
 name = "opentelemetry-api"
 version = "1.44.0"