Use the canonical Unicode aware slugifier for id prefixes

Fixes issue 3352.

_id_prefixes reimplemented id segment slugification with its own
ASCII only regex, so any path segment made of non Latin characters
(Korean, CJK, Cyrillic and so on) collapsed to nothing instead of
being preserved. _defines_id, the only real caller, uses these
prefixes to recognize when a node's own source_file is the file its
id encodes, and _collision_rank already implements the definer wins
rule this issue asks for. With the wrong prefixes, a node minted from
a non ASCII path never matched, so a genuine defining page lost the
definer wins tiebreak and the survivor fell through to plain arrival
order, exactly the symptom this issue reports.

Swapping to normalize_id, the same recipe every real extractor mints
an id with, makes the reconstructed prefixes match the ids that are
actually minted for such a file.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017qfdzgbA5KedGEjD1AayNh
(cherry picked from commit e618f332f6)

graphify/dedup.py

@@ -266,7 +266,6 @@ def _is_code(node: dict) -> bool:
 
 # ── ID collisions ─────────────────────────────────────────────────────────────
 
-_ID_SEGMENT = re.compile(r"[^a-z0-9]+")
 _EXTENSION = re.compile(r"\.[^./]+$")
 
 
@@ -277,10 +276,17 @@ def _id_prefixes(source_file: str) -> set[str]:
     path, each segment slugified and joined with ``_``. Every trailing slice of the
     path counts as a prefix: the stored path may be absolute or repo-relative, and
     graphs built under the pre-#1504 scheme keyed off the bare filename stem.
+
+    Each segment is slugified with ``normalize_id`` (#3352), the same
+    Unicode-aware casefold-then-NFKC-then-``[^\\w]+`` recipe every real ID is
+    minted with. An ASCII-only slug here silently dropped every non-Latin
+    character (Korean, CJK, Cyrillic, ...) instead of preserving it, so a
+    node's own defining file was never recognized as the file that ID
+    encodes and the definer-wins collision rule (see ``_defines_id``,
+    ``_collision_rank``) fell through to arrival-order for any such path.
     """
     stem = _EXTENSION.sub("", source_file.replace("\\", "/"))
-    segments = [s for s in (_ID_SEGMENT.sub("_", p.casefold()).strip("_")
-                            for p in stem.split("/")) if s]
+    segments = [s for s in (normalize_id(p) for p in stem.split("/")) if s]
     return {"_".join(segments[i:]) for i in range(len(segments))}