[TechNomadCode]

Slice 16: the assistant's text fades in instead of appearing in a jump (opencode's markdown-word-enter, a 180ms opacity fade).

• Only an answer that arrives after the chat showed fades; a finished answer, a conversation brought back after a reload, and everything under reduced motion show at once.
• Each update's words fade as one span per run: a reply that arrives whole, as on staging, fades once; the fake model's words fade by groups. Words already shown never fade again, even when a table taking shape re-renders them.
• The conversation stays out of any live region, so screen readers hear nothing new.
• The accessibility check now waits until no word is fading: axe read a word mid-fade as low contrast.

Changes nothing in src/server or src/lib, so the measurement lane needn't wait for it.

Checks, local: verify (464 unit tests, 10 new) and test:e2e (61, 2 new) passed in two full runs back to back.

Also settles the next piece's copy button on opencode's form (docs only).