style(rl): F1.3 code review fixes — comments + spec annotations
Code-quality review found 1 Important + 4 Minor; applied all 5:
- I1: restored `(issue #9, drift-free)` cross-link in Phase 4 header
- M1: added explicit launch profile in header `Grid=(1,1,1), Block=(1,1,1), smem=0`
- M2: comment explaining `count` reuse in Phase 3 (Welford state retained in registers)
- M3: inline rationale for `kelly == 0.0f` and `cooldown == 0.0f` exact equality
- M4: extended Welford-bootstrap comment with statistical floor justification
(exempt from ISV-promotion per "physics/math constants" rule)
Zero functional change — comments only; cubin rebuilds identical bytes.
6ded2c55c2