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.
ExprTyper.inferType had no `.force_unwrap` arm, so `mk()!` typed as
`.unresolved`. The bind-first form (`v := mk()!; v.field`) worked because
lowerForceUnwrap produces a correctly typed value stored in a slot, but the
chained `mk()!.field` re-derives the receiver type via inferExprType and got
`.unresolved` — the struct-field lookup failed, the field read emitted as
`undef` (garbage), and `mk()!.method()` failed to resolve the method.
Add a `.force_unwrap` arm resolving the operand's optional child type. One
arm fixes every chained form — field, nested `opt!.a.b`, `opt!.method()`
(pointer + value receiver), and `opt![i]` all route receiver typing through
inferExprType.
Regression: examples/0905-optionals-unwrap-field-chain.sx — garbage / compile
error pre-fix, all correct after.
