docs: add # Domain role sections to public items (0.15.1)

[folkengine]

Docs

• docs: add # Domain role sections to 219 public types and free functions across src/ (113 files, +1116/−2)
• Table and PokerSession tagged consistency boundary (DDD: aggregate), each with the invariants the code keeps
• Storage, I/O, serde and terminal items left untagged on purpose as shell code
• Fixed a redundant doc link in src/games/mod.rs and a stray // line inside a doc test in src/bot/draw_equity.rs

Config

• Version bumped 0.15.0 → 0.15.1 in Cargo.toml, Cargo.lock refreshed
• CHANGELOG.md entry added under ## [0.15.1] - 2026-09-16