fix(understand): the bare Russian "to" before a panel is a wiring callout

A Russian P&ID often closes a load's text with the panel it is wired to:
'... кВт' on one line, then 'к CP1' ('to CP1') or 'к щиту CP-2' ('to
switchboard CP-2') on the next. wiring_target knew 'подключение к ...' but
not the bare preposition. On the field P&ID most loads therefore had no
panel and no measurable cable.

The preposition к / ко now counts when it is a whole word and the panel is
the next word, optionally after щиту / шкафу / панели. The к of кВт is
never read as the preposition. The new test failed before the change.

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

engineering/understand/labels.py

@@ -135,6 +135,15 @@ _WIRING_PHRASES = (
 )
 #: Turkish puts the panel first: ``CP1 panosuna`` ("to the CP1 panel").
 _WIRING_PHRASES_AFTER = ("panosuna", "panosundan")
+#: The bare Russian preposition к / ко ("to") with the panel as the next word,
+#: optionally after "щиту" / "шкафу" / "панели" (switchboard / cabinet / panel):
+#: a Russian P&ID closes a load's text with ``к CP1``. Only a whole word counts,
+#: so the к of кВт is no preposition.
+_RU_TO_PANEL = re.compile(
+    r"(?:^|\s)ко?\s+"
+    r"(?:(?:щиту|шкафу|панели)\s+)?",
+    re.IGNORECASE,
+)
 
 
 def plain(text: str | None) -> str:
@@ -295,7 +304,9 @@ def wiring_target(text: str | None) -> str | None:
 
     ``"Wiring to CP1"`` -> ``"CP-1"``; ``"подключение к шкафу CP-1"`` ->
     ``"CP-1"``; ``"CP 2 panosuna"`` -> ``"CP-2"`` (Turkish names the panel
-    first). None when the text has no wiring phrase or no panel beside it.
+    first); ``"... кВт\\nк CP1"`` -> ``"CP-1"`` (the bare Russian "to", the
+    panel as the next word). None when the text has no wiring phrase or no
+    panel beside it.
     """
     body = plain(text)
     lowered = body.lower()
@@ -311,4 +322,8 @@ def wiring_target(text: str | None) -> str | None:
             matches = list(_PANEL_RE.finditer(fold_lookalikes(body[:at])))
             if matches:
                 return f"{matches[-1].group(1)}-{matches[-1].group(2)}"
+    for to in _RU_TO_PANEL.finditer(body):
+        panel = _PANEL_RE.match(fold_lookalikes(body[to.end() :]))
+        if panel is not None:
+            return f"{panel.group(1)}-{panel.group(2)}"
     return None