Update README with new node sections (AutoTuner, Merge Selector,
Save/Load Tuner Data), diff cache and VRAM budget details, ACE-Step
architecture support. Add AutoTuner tag to banner SVG. Add 4 new
entries to development timeline (AutoTuner, Merge Selector + Save/Load,
Diff Cache, VRAM Budget).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>