Arcadic.Vector — dense vector search over ArcadeDB LSM_VECTOR (index DDL +
neighbors/fuse builders), tenant-blind, params-only, value-free-validated.

- Bump version 0.1.0 -> 0.2.0 (additive feature).
- CHANGELOG: [Unreleased] -> [0.2.0] with the full Arcadic.Vector entry incl.
  the similarity-dependent distance / fuse-score notes.
- README: new "Vector search" section + highlight; usage-rules: public-surface entry.