Track mechanical compiler warning cleanup tranche

[somethingwithproof]

Context

PR #497 introduces low-risk mechanical warning cleanup changes.

Scope

• const-correctness and qualifier cleanup
• unused/shadow/newline-eof mechanical fixes
• no behavioral feature changes

Acceptance Criteria

• strict local build remains green
• make check remains green
• warning count does not regress from PR baseline

Linked PR

• chore(warnings): mechanical low-risk cleanup pass #497