fix: allow Unicode in sanitize_name() — Latvian, CJK, Cyrillic (#637) (#683)

* fix: allow Unicode in sanitize_name() — Latvian, CJK, Cyrillic names (#637)

_SAFE_NAME_RE was ASCII-only ([a-zA-Z0-9]), rejecting valid Unicode
names like "Jānis" or "太郎". Changed to \w which matches Unicode
word characters (letters, digits, underscore) in Python 3.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: tighten Unicode regex, add sanitize_name tests

Use [^\W_] for first/last char to allow Unicode letters/digits but
reject leading/trailing underscores (Copilot feedback). Add 7 tests
covering Latvian, CJK, Cyrillic, path traversal, and edge cases.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

mempalace/config.py

@@ -16,7 +16,7 @@ from pathlib import Path
 # in file paths, SQLite, or ChromaDB metadata.
 
 MAX_NAME_LENGTH = 128
-_SAFE_NAME_RE = re.compile(r"^[a-zA-Z0-9][a-zA-Z0-9_ .'-]{0,126}[a-zA-Z0-9]?$")
+_SAFE_NAME_RE = re.compile(r"^(?:[^\W_]|[^\W_][\w .'-]{0,126}[^\W_])$")
 
 
 def sanitize_name(value: str, field_name: str = "name") -> str: