Replace direct `Instance.provide` usage with `WithInstance.provide` across
source modules and test files to decouple runtime context provisioning
from the core Instance singleton.
- Update kilo-sessions, remote-sender, roll-call, and plan-followup source
- Remove unused `Instance` imports where only `WithInstance` is needed
- Drop unnecessary `init` param from indexing-worktree test calls
- Add missing `WithInstance` import in fixture-dependent test files
Imanol Maiztegui
128df55d6b