Remove dead code - constructor variants that had no callers:
- new_with_readme()
- new_autonomous_with_readme()
- new_with_quiet()
These were thin wrappers around new_with_mode_and_readme() that were
never used externally. All 5 remaining constructors have verified callers.
Results:
- lib.rs reduced from 2817 to 2797 lines (-20 lines)
- Eliminated code-path aliasing: 8 constructors → 5 constructors
- All g3-core tests pass
- Full workspace compiles cleanly
Agent: fowler
7d17b436f9