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.
lowerComptimeCall stamped the caller's source onto fixed comptime `$`-params
so their substituted bare names resolve in the caller's visibility context,
but the variadic comptime pack branch (`..$args`) recorded the pack-arg slice
without stamping. Those nodes are later re-lowered via packArgNodeAt under the
defining-module pin, so a caller-owned helper in a formatted-arg position
(`std.print("{}", caller_fn())`) was checked against the metaprogram's module
and rejected as "not visible". Stamp every pack-arg node with the caller source,
mirroring the fixed-param treatment — completing Problem 1 for pack args.
Regression: examples/0739-modules-comptime-pack-arg-caller-context.sx
(two caller-owned s64 helpers in std.print pack positions; fail-before both
"not visible", pass-after prints "42 7"). No exemption flag, no silent default.
