docs: changelogs and phase restructure for the models refactor (phase 8)
Breaking-change entries with migration guides: pi-ai (compat
entrypoint, Provider -> ProviderId, api module moves, new Models/
provider/auth API), agent (required AgentHarnessOptions.models,
compaction signatures, structural StreamFn), coding-agent (extension
author note: runtime unaffected via loader compat alias).
models.md: Phase 7 closed out (import switch landed with phase 5; the
gated bullets move to a new Phase 9 ModelManager-migration outline:
per-session Models, AgentSession streaming, AuthStorage replacement,
login UI on OAuthAuth, cloudflare cleanup, internal compat removal,
compat deletion).
Mario Zechner
10a575b76b