Model-picker audit follow-through — closes the remaining pieces of the
"switch one session, switches everywhere / can't tell whose session this
is" report class:
- tui_gateway: `config.set key=fast` with a session no longer writes the
global agent.service_tier to config.yaml (sibling of the earlier
`reasoning` scoping fix). It pins create_service_tier_override
("priority" / "" for explicit normal) so lazy builds and rebuilds keep
the choice; the desktop's per-model presets were rewriting the global
tier on every model pick. Fast-support validation now checks a draft's
picked model, and `config.get key=fast` reads the pre-build pin.
- desktop: owning-profile tag (initial chip + tooltip/aria label) on
pinned rows and search results in the All-profiles sidebar, and on the
chat header once a second profile exists (#66003).
- desktop: composer model pill shows a pin dot + tooltip when a manual
sticky pick is overriding the Settings default for new chats (#62055).
Closes#66003. Addresses #62055.
