Memory save stores "the user" instead of the user's name ("Priya, the user's sister, lives in Mumbai") #475

Seen while testing #471 (#463) on qwen3:8b: the memory-save tool stored "Priya, the user's sister, lives in Mumbai." instead of using the user's name ("Priya, Maya Rao's sister…"). Memories that say "the user" read oddly on the Memory screen, and they're harder for the subject matching from #471 to tie to the user.

Fix: when a fact is saved, replace "the user" / "the user's" with the user's configured name (and handle "user's"), the way other places substitute the name. Add tests.

Done when: a test saving "Priya, the user's sister, lives in Mumbai" stores "Priya, Maya Rao's sister, lives in Mumbai".