Add shared agent-level USER_PREDEFINED.md file for predefined agents to define
baseline user-handling rules (owner info, audience, language, communication norms)
that apply to ALL users. Individual USER.md per-user supplements but never overrides.
- Seed USER_PREDEFINED.md template in SeedToStore for new predefined agents
- Backfill existing agents via ensureUserPredefined in summon/regenerate flows
- AI optionally generates/updates the file when description mentions people/user context
- Add to context file interceptor, RPC allowlist, and system prompt injection
- Update summoning modal with optional file progress tracking
- Show estimated token count (Unicode-aware) instead of bytes in file sidebar
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
