Saving a fact about another person overwrites the user's own memory ("Maya's sister Priya lives in Mumbai" replaced Maya's home) #463

Found while testing #453 on a fresh engine.

POST /api/memories with "Maya Rao's sister Priya lives in Mumbai." overwrote the existing memory "Maya Rao moved from Pune to Bengaluru…". The engine log said corrects fact 2, updated without asking the model, from the residence shortcut in sentient/memory/facts.py (~1490). In a second run, a similar cross-person overwrite happened again, probably through the model's CUD decision.

docs/API.md says an update only replaces a fact about the same person, and facts that name someone else are never offered to the model. The residence shortcut doesn't respect that, and the model path may not either.

Fix:

• the new-residence shortcut must only fire when the subject of the new fact is the same person as the old one (Maya vs "Maya's sister Priya");
• check the CUD candidate filter for possessive and relative phrasing ("X's sister", "my friend Y", "her colleague");
• add tests: "Maya's sister Priya lives in Mumbai" ADDs and leaves "Maya lives in Bengaluru" alone; "Maya moved to Mumbai" still UPDATEs it.

Done when: in a real run on qwen3:8b and via REST, facts about other people never replace the user's own, and a true correction still does.