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.
Address Phase C review (C-1, C-2): make CallResolver.plan's SelectedFunc the
single shared call author consumed by the lower-call sites instead of each
re-resolving; route free-fn value-receiver UFCS through the selector in plan so
plan typing and lowering pick the same author under a flat same-name collision.
Adds regression 0740-modules-flat-same-name-ufcs-typing.
Salvaged from a worker killed at the wall during its final gate step; manager
verified the gate at ground truth (zig build test exit 0; run_examples 476/0 with
0722-0735 + 0740 ok; m3te ios-sim exit 0).