* fix: make entity_registry.research() local-only by default
research() previously called _wikipedia_lookup() unconditionally,
sending entity names to en.wikipedia.org on every uncached lookup.
This violates the project's local-first and privacy-by-architecture
principles documented in CLAUDE.md.
Changes:
- research() now returns "unknown" for uncached words by default
- New allow_network=True parameter required for Wikipedia lookups
- Wikipedia 404 now returns "unknown" instead of asserting "person"
with 0.70 confidence, preventing entity registry poisoning
- Added privacy warning docstring to _wikipedia_lookup()
- Added tests for local-only default, opt-in network, 404 handling,
and cache-not-persisted-on-local-only behaviour
Refs: MemPalace/mempalace#809
* fix: improve research() cache read path and deduplicate test mocks
- Use .get() instead of .setdefault() for cache reads in research()
so the local-only path never mutates _data unnecessarily
- Move .setdefault() to the network-write path only
- Use result.setdefault() for word/confirmed keys to ensure
consistent return shape across all _wikipedia_lookup error paths
- Extract duplicated mock_result dict into _MOCK_SAOIRSE_PERSON
constant shared by 3 test functions