fix(desktop): Clear stale chat notices

[kotevcode]

Description

Clears transient desktop chat notices whenever the user changes conversations or switches the selected model. This keeps paid-service payment_required messages and other chat errors from sticking around after the context changes.

This intentionally uses the simpler behavior: errors/payment requests are dismissed on conversation/model change rather than restored per prior conversation.

Release Notes

• Fixed payment-required messages and payment cards sticking around after switching chats or models.
• Fixed stale chat error messages remaining visible after moving to a different conversation.

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Chore (maintenance tasks, refactoring, or non-functional changes)

Checklist

• My code follows the code style of this project
• I have added the necessary documentation (if appropriate)
• I have added tests (if appropriate)
• Lint and unit tests pass locally with my changes

Verification

• pnpm --filter @antseed/desktop run typecheck:renderer
• pnpm exec tsx --test apps/desktop/src/renderer/modules/chat.peer-routing.test.ts
• pnpm --filter @antseed/desktop run build:renderer