feat(understand): cable_takeoff - one row per load, rounded to the metre

cable_rows reads each load's power, phases, voltage, neutral and VFD from the
P&ID's electrical texts near its tag, and its panel from the layout's wiring
callouts (else the P&ID's), names normalised CP 1 -> CP-1. The length is the
Manhattan distance on the layout from the tag to its panel, and the cable
ROUNDUP(length x (1 + allowance)) to the metre, on the length rounded to
1e-6 m so binary noise never buys a metre. Power is never invented: a load
with no stated kW keeps an empty cell and an open item. Without a layout the
lengths stay empty with an open item per row. Room and panel totals count a
panel package's power once, never its children's as well; the rule is on the
method sheet. Sections only from the caller's section_rules - no standard
table exists here.

The workbook gains the cable shape (Metraj, Ozet by room and panel, Kontrol
as the open-items list, Metodoloji) in the same three languages;
cable_takeoff joins SECTION 27. Inventory regenerated; README snapshot 243
tools (238 advertised); registry snapshot analysis: 14.

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

engineering/understand/draw.py

@@ -15,9 +15,15 @@ import math
 from engineering.understand.network import build_network
 from engineering.understand.report import check_lang, write_workbook
 from engineering.understand.snapshot import take_snapshot
-from engineering.understand.takeoff import check_pipe_options, pipe_rows
+from engineering.understand.takeoff import (
+    cable_rows,
+    check_allowance,
+    check_pipe_options,
+    check_section_rules,
+    pipe_rows,
+)
 
-__all__ = ["run_pipe_takeoff"]
+__all__ = ["run_cable_takeoff", "run_pipe_takeoff"]
 
 
 def _check_tol(tol) -> float:
@@ -84,3 +90,30 @@ async def run_pipe_takeoff(
         else None
     )
     return result
+
+
+async def run_cable_takeoff(
+    backend,
+    *,
+    pid_path: str | None = None,
+    layout_path: str | None = None,
+    output: str | None = None,
+    lang: str = "en",
+    allowance: float = 0.20,
+    section_rules=None,
+) -> dict:
+    """`cable_rows` over a P&ID and an optional layout, plus the workbook when `output` is named."""
+    check_lang(lang)
+    allowance = check_allowance(allowance)
+    rules = check_section_rules(section_rules)
+    pid = await take_snapshot(backend, pid_path)
+    layout = await take_snapshot(backend, layout_path) if layout_path else None
+    result = await asyncio.to_thread(
+        cable_rows, pid, layout, allowance=allowance, section_rules=list(rules) or None
+    )
+    result["files"] = (
+        await asyncio.to_thread(write_workbook, result, kind="cable", lang=lang, path=output)
+        if output
+        else None
+    )
+    return result