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 shared compile-time integer folder (`evalConstIntExpr`) accepts an
integral float literal/const as an integer leaf (`[4.0]` → 4) and then
applied INTEGER arithmetic to the whole expression — so `5.0 / 2.0` folded
as `divTrunc(5,2)` = 2 instead of float division (`2.5`). The bug fired at
all FIVE unified-rule sites (typed local, field default, param default,
typed const, array dimension), because the typed sites evaluate through
`evalConstFloatExpr` (which delegates the node to the int folder) and the
count sites through `foldCountI64` (int folder first).
Fix at the single root: `evalConstIntExpr`'s `.div` arm refuses to fold a
division whose lhs/rhs is float-valued (`isFloatValuedExpr`), so the value
surfaces through `evalConstFloatExpr` + the unified rule — an integral
quotient (`6.0 / 2.0` → 3) folds, a non-integral one (`5.0 / 2.0` = 2.5,
mixed `5 / 2.0`, float-const `F / G`) errors. Genuine integer `/` (`5 / 2`
→ 2) is unchanged; `*`/`+`/`-` need no guard (they agree between int and
float for the integral operands the int folder ever sees).
`isFloatValuedExpr` judges a const-leaf by VALUE (`moduleConstIsFloatTyped`
recurses into the const's value with the existing cycle-guard frame), so an
untyped float-EXPRESSION const (`ME :: 4.0 + 1.0`, placeholder type s64) is
caught at both the count path and — via `foldComptimeFloatInit`'s guard —
the typed-binding path. A backtick RAW receiver (`` `f64.epsilon ``) is a
field read, not a float limit (is_raw check, issues 0092/0093).
Regression: examples/1147 (negative — `5.0 / 2.0` errors at all five sites
plus untyped float-EXPR const div); 0168 extended (positive — `6.0 / 2.0`,
`12.0 / 4.0`, `[6.0/2.0]`, `xx (5.0/2.0)` → 2); unit tests "the int folder
refuses a FLOAT division" and "moduleConstIsFloatTyped judges a const by
VALUE". specs.md + readme.md state the float-`/` rule.
