STYLE: Complete the declare-then-assign sweep beyond #6014's 42 files

[hjmjohnson]

#6014 converted declare-then-assign to initialization-at-declaration across 42 files. A follow-up scan indicates the sweep is incomplete, but the residual count needs restating with an explicit predicate before the work is scoped.

Count — and why the previously circulated number is wrong

A local note carried an estimate of "~65 more candidates". That figure is
unsupported and should not be used. Re-scanning during a 2026-07-29 audit
produced substantially fewer:

Predicate	Sites
Strict adjacency (declaration immediately followed by assignment)	21
Relaxed (skipping intervening comments; wider type set)	31

These were derived by an automated pass and have not been independently
reproduced. The first work item is therefore to fix the predicate and publish
it, so the number is re-derivable the way #6388's scanner is.

Proposed work

1. State the exact predicate (which types, what counts as "adjacent",
   whether comments/blank lines break the pair) and publish the scanner
   alongside the count.
2. Convert the sites the predicate selects, respecting the hazard in the
   companion documentation issue: T x = expr; is construction, not
   assignment, so tests that deliberately exercise operator= must keep the
   two-line form.
3. Skip any site where the variable is later mutated, or use the explicit-type
   form rather than auto.