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.
Pack/tuple spread now parses in tuple-value `(..xs)` / `(..xs.field)`,
tuple-type `(..F(Ts))` / `(..F(Ts.Arg))`, call-arg `f(..xs)` (already),
and closure-sig `Closure(..Ts)` / `Closure(..sources.T)` positions.
Design: the uniform spread node is the existing `spread_expr` (its
operand sub-expression carries the projection `xs.field` and
type-application `F(Ts)` shapes) rather than a new PackExpansion node —
call-arg slice-spread (`..arr`) and pack-spread (`..pack`) are
syntactically identical, so they must share one node, and spread_expr
already serves it with working slice lowering. Closure-sig packs gain
`ClosureTypeExpr.pack_projection` alongside the existing `pack_name`.
Parser-only; sema/lowering land in Phase 2. 6 new parser unit tests +
examples/probes/pack-expansion-parses.sx. Build + 225-suite green.
