Mechanical sweep of all .sx sources and plan docs (PLAN.md, current/,
.agents/) for the sx language rename (s8/s16/s32/s64 -> i8/i16/i32/i64).
Verified: make build + make test, 14/14.
Stand up the foundation every later step depends on:
- Source layout: src/, src/infra/, tests/, examples/ (.gitkeep markers).
- Makefile: `build` compiles the smoke program via $SX, `test` runs the
runner over tests/**/*.sx, `publish-example` placeholder (real in P3.4).
Compiler located via `SX ?= /Users/agra/projects/sx/zig-out/bin/sx`.
- tests/run.sh: POSIX-sh runner; discovers tests/**/*.sx, runs each via
`$SX run`, prints ok/FAIL, exits 0 only when all pass (errors on zero
tests so the gate is never silently empty).
- tests/smoke.sx: passing smoke test importing modules/std.sx — proves
toolchain wiring end-to-end (std resolves via the binary's own location).
- .gitignore: ignore build/ artifacts.
