fix(write-path): disclose cross-language prior art instead of hiding it

Closes #2244. Retrieval matches on concept, and concepts are language-agnostic:
asking about a TypeScript union-find scores 0.72-0.73 against a PYTHON snippet,
comfortably over the 0.68 bar. That is useful — a different-language solution
gives you the shape even when the code isn't reusable — but the menu line said
nothing about it, so the reader either dismissed a good structural reference or
pasted Python into a .ts file.

Worth noting this predates the concept-query change: raw TS code already matched
the Python snippet at 0.73, because the embedder reads identifiers and structure
semantically rather than syntactically. The fail state has been shipping quietly;
#2242 only made it an intended use rather than an accident.

- knowledge._note_to_item projects `language` from the data mirror, same shape as
  the existing verification projection — a plain column read, no body parsing.
- The semantic arm carries language through on the item it builds; it is the arm
  where these arise, since a snippet recorded AT the path you're editing is
  almost never in another language.
- _prior_art_line folds it into the marker: [similar 0.72 · python]. Together
  with the score rather than after the title, because the two jointly are the
  judgement being offered.
- One explanatory line is added to the menu, and only when something on it is
  actually tagged.

Two deliberate calls:

LABEL, DON'T FILTER. A stricter threshold for foreign-language hits would
suppress exactly the shape-borrowing this exists for. They were never the
problem; their being undisclosed was.

ONLY CLAIM A MISMATCH YOU CAN ESTABLISH. _foreign_language returns "" when either
side is unknown — unrecognised extension, or a snippet with no recorded language.
A wrong "· python" is worse than no tag. Same-language hits stay unlabelled, so
the common case keeps a clean line and the preamble stays off the menu entirely.
Operator-typed language names fold through an alias table first (py/python3 →
python, tsx → typescript, c++ → cpp); unrecognised names pass through lowercased,
which still makes an unknown-but-equal pair compare equal.

Trap found while building: _note() in the tests is a MagicMock, so `note.data`
auto-created a truthy mock that would have rendered its repr into a menu line.
Both test helpers now set data = None explicitly.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

src/scribe/services/knowledge.py

@@ -211,6 +211,15 @@ def _note_to_item(note: Note) -> dict:
     # body parsing and stays a plain projection of the column. Omitted entirely
     # when unchecked, so "no key" and "never verified" don't become two states
     # the client has to tell apart.
+    # Snippet language, same reasoning as the verdict below: a plain projection of
+    # the `data` mirror, no body parsing. Needed because a prior-art hit in a
+    # DIFFERENT language than the file being written is useful as the shape of a
+    # solution but must not be mistaken for code to paste (#2244) — and the caller
+    # can only say "different" if the language is on the item.
+    language = (note.data or {}).get("language") if note.data else None
+    if language:
+        item["language"] = language
+
     verdict = (note.data or {}).get("verification") if note.data else None
     if verdict and verdict.get("status"):
         item["verification"] = {