v2.1.0

v2.1 — diagnostics code frames, watch DX, init-adopt, minifier

- Unified code-frame diagnostics across build/watch/dev/minify/bundle/pack
- --max-errors, --json line:col, clear-on-rebuild (--no-clear), persistent
  error banner, --bell fail<->pass cue
- rotor init adopts existing projects (config-only, no clobber, --config);
  doctor warns + suggests rotor init when rotor.toml is missing
- Minifier: convert_index_to_field (t["x"] -> t.x), number-glue separator
  correctness fix, and rotor build --minify (opt-in, byte-parity safe)