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 two not-yet-lowered fn_ast_map paths in resolveCallParamTypes (the
qualified `ns.f(...)` call and the plain free-fn call) resolved each
param type in the CALL SITE's visibility context, so a namespaced
import's param type that is bare-visible only in its own module
diagnosed "type 'X' is not visible" at calls whose caller never names
the type bare. Route both through the E4 source pin
(resolveParamTypeInSource), as the method paths already do.
A generic callee's bare T leaves are not nominal names in that module:
astCalleeParamTypes installs the call's inferred $T -> concrete
bindings (the one binding builder) before resolving, or the pin turns
the unbound leaf into "unknown type 'T'" (regressed examples/0129
through math/scalar.sx's clamp).
Regression: examples/0840 (namespaced fn with a module-bare param
type; failed "not visible" pre-pin).
