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.
The const-decl alias-registration path treated a qualified generic head
(`ABox :: a.Box(s64)`) only as a gate exemption, then read the bare last-wins
`struct_template_map` — so `ABox` and `BBox` both instantiated whichever
same-name template won globally (both size 16). attempt-9 routed the annotation
head sites through `qualifiedStructTemplate`; this applies the same selection to
the two alias-registration branches (.call and .parameterized_type_expr) before
the bare fallback, and extracts the shared instantiate-and-register logic into
`registerGenericStructAlias`.
ABox :: a.Box(s64) now resolves to a's template (size 8); BBox :: b.Box(s64) to
b's (size 16). Regression 0773 pins it (fail-before alias a=16 b=16, after a=8
b=16).
