fix(desktop): reseed new chats from profile defaults

[deniqlab]

Fixes the fresh-new-chat model seeding regression reported in #65300 / related #50821.

What changed

• Force the fresh new-session draft sync path to reseed the composer model/provider from the profile/global default instead of reusing the prior sticky selection.
• Add a regression test for the fresh-draft reseed path.
• Strengthen the model-controls test to assert the provider reseeds too.

Verification

• npm test -- src/app/contrib/hooks/use-background-sync.test.tsx src/app/session/hooks/use-model-controls.test.tsx ✅
• git diff --check ✅
• npm run lint -- src/app/contrib/hooks/use-background-sync.ts src/app/contrib/hooks/use-background-sync.test.tsx src/app/session/hooks/use-model-controls.test.tsx ✅ (repo-level warnings only)
• npm run typecheck ❌ blocked by baseline missing/incompatible desktop dependencies in this environment
• npm run build ❌ blocked by baseline missing/incompatible assistant-ui exports in this environment

Notes

This branch is published from fork/deniqlab due push permissions on the upstream repo.

[teknium1]

Thanks for the focused regression test and narrow implementation.

Problems

• apps/desktop/src/app/contrib/hooks/use-background-sync.ts:132 changes a fresh draft to call refreshCurrentModel(true). On current main, force is intentionally reserved for profile swaps: apps/desktop/src/app/session/hooks/use-model-controls.ts:38-56 preserves a non-empty composer selection, while apps/desktop/src/app/session/hooks/use-session-actions/index.ts:210-215 explicitly keeps that selection for new chats.
• The referenced #62055 also reports that a Settings-selected model can be missing from the composer picker. This change resets the selection but does not address that catalog/availability path.

Suggested changes

• Keep the non-forced fresh-draft refresh unless maintainers choose to change the sticky-composer contract introduced in cb6b4127e.
• If targeting #62055, re-scope to the composer model-options path and test that the Settings-selected model is available and usable there.

Automated hermes-sweeper review.

[teknium1]

true overrides the deliberate sticky-composer contract: startFreshSessionDraft keeps the previous model/provider for new chats (apps/desktop/src/app/session/hooks/use-session-actions/index.ts:210-215), and refreshCurrentModel reserves force for profile swaps (apps/desktop/src/app/session/hooks/use-model-controls.ts:38-56). Please retain the non-forced call unless that product behavior is intentionally being changed.

[OutThisLife]

Closing as a duplicate of #67207 (same author, same fix for #65300 — reseed fresh new-chat composer model/provider from profile defaults).

Please continue on #67207; reopen this only if that PR is abandoned and this branch is the one to land.