Phase 1C changes:
- ASCII art logos: CODEBUFF → PLANEXE (full + small variants)
- Text fallback: 'Codebuff CLI' → 'PlanExe CLI'
- CLAUDE_OAUTH_ENABLED: false → true (Simon can use Claude subscription)
- Kept: OAuth client ID, beta headers, system prompt prefix (required by Anthropic)

Files changed:
- cli/src/login/constants.ts (ASCII art)
- cli/src/hooks/use-logo.tsx (text fallback + brand name)
- common/src/constants/claude-oauth.ts (OAuth flag)

Authored by Bubba. Plan by Egon (plans/planexe-cli-wrapper-plan.md).