fix: use permissive validator for KG entity values

[sha2fiddy]

Summary

• Adds sanitize_kg_value() in config.py — a permissive validator for knowledge graph subject/object fields that allows punctuation (commas, colons, parentheses, slashes, #, etc.) while still blocking null bytes and enforcing the 128-char length limit
• Updates mcp_server.py KG tools (kg_add, kg_invalidate, kg_query, kg_timeline) to use sanitize_kg_value for subject/object/entity fields; predicates still use the strict sanitize_name
• sanitize_name was designed for wing/room names with filesystem constraints — KG entity values live in SQLite and don't need those restrictions

Closes #455

Test plan

• New tests for sanitize_kg_value: accepts commas, colons, parens, slashes, #, Unicode; rejects empty, whitespace-only, null bytes, over-length
• Full test suite passes (875 tests)
• ruff check clean
• ruff format --check clean