Surface rename of the signed integer family: s1..s64 become i1..i64
(u1..u64, usize, isize unchanged). 'string' keeps the s-prefix arm in
name classification; width parsing moves to the i-prefix arm next to
isize.
Internal TypeId tags follow the surface (.s8/.s16/.s32/.s64 ->
.i8/.i16/.i32/.i64), as do mono-key mangle fragments (ptr_i64,
tu_i64_bool) and all display/diagnostic formatting (i{d}).
Migrated in the same sweep: stdlib + examples + issue repros + FFI C
companions (shared symbol names like ffi_id_i64), expected
stdout/stderr/ir snapshots, specs.md, readme.md, CLAUDE.md/AGENTS.md,
implementation_plan.md, docs/, issue writeups. Vendored stb_image and
historical flow state left untouched.
zig build test: 426/426; examples suite: 595/595.
resolveBareCallee's flat-collect branch counted ALL same-name authors —
including #foreign / generic / builtin / #compiler — before the
isPlainFreeFn filter, so two flat-imported modules each #foreign-ing the
same libc symbol under one sx name returned `.ambiguous` and errored,
instead of falling to `.none` and the existing first-wins foreign path
(master behavior). Filter authors to plain free functions DURING
collection, before the count/ambiguity determination: a non-plain
collision now yields 0 reroutable authors -> `.none`; genuine plain-fn
collisions still yield >= 2 -> `.ambiguous` (0724 unchanged). The
now-redundant single-author isPlainFreeFn check is dropped.
Regression: examples/0729-modules-flat-same-name-foreign — two flat FILE
imports each #foreign the same libc "abs" under name `absval`; a bare
call resolves first-wins and runs (exit 0). Fails-before on this branch
(ambiguity error), passes-after.
