docs(readme): cut to vitrine (481 → 111 lines)

Apply the new codechu-org STANDARDS §7.1 vitrine rule + LIBRARY.md
§6.1 skeleton to the cli README. The root README is now a
showcase, not a manual.

Kept (vitrine):
- Hero ASCII banner + a second inline demo block.
- Badges, tagline, value prop.
- Install with sibling-dep note.
- ONE quick example covering ProgressBar + Spinner + confirm.
- Capability bullets (6 lines, not API tables).
- Documentation links → docs/.
- Family table trimmed to the 5 closest siblings.
- Credits, License.

Moved to docs/CUSTOMIZE.md (new):
- Custom color palette + force enable/disable.
- Custom progress bar templates.
- Emoji registration.
- Keymap override.
- Internationalization (translator hook).
- ASCII-art banners + LOGOS registry.
- Style discovery via `python -m codechu_cli demo`.
- Style-name stability promise.

API reference table dropped from README — docs/API.md (838 lines)
is the authoritative reference.

Author: obarlik