Co-Authored-By: Thuong Huynh <admin@huynhthuong.online>

- Replace GitHub Copilot CLI content with Command Code product branding
- Add feature grid (Models, Taste, Extend, Code, Review, Bugs)
- Add 'How taste works' section with taste-1 neuro-symbolic system
- Add quickstart guide, core concepts, CLI reference
- Add common workflows with practical examples
- Add docs navigation table, skills, MCP, and Studio sections
- Add troubleshooting guide and next steps

Co-Authored-By: Thuong Huynh <admin@huynhthuong.online>

Co-Authored-By: Hoai thuong Nguyen van <admin@huynhthuong.online>

Adds a new `devin` shell script that provides 4 invocation modes:
- `devin`                    — interactive REPL (no prompt)
- `devin -- <prompt>`        — REPL with initial prompt
- `devin -p "prompt"`        — single-turn, print to stdout and exit
- `devin -p -- <prompt>`     — single-turn with -- separator

Also supports --model, --headless, --plan flags.
Includes a built-in stub REPL when no copilot backend is installed.
Updates README with devin CLI reference.

Co-Authored-By: Thuong Huynh <admin@huynhthuong.online>

- Add -- separator before prompt in print-mode dispatch to prevent
  flag-like prompts (e.g. '--version') from being parsed as backend flags
- Set HEADLESS=true when MODE=print after parse_args, so build_cmd()
  handles it once instead of duplicating --headless in the dispatch
- Declare 'line' as local in builtin_repl for scope hygiene

Co-Authored-By: Thuong Huynh <admin@huynhthuong.online>

docs: add pull request template