Add the core distribution domain model under src/domain/ (App, Release,
Artifact, Channel, AuditEvent + Platform/Visibility/ValidationStatus/
RolloutPolicy enums) and a boundary validator that returns one distinct
typed ValidationErr per failure class (BadSlug, EmptyVersion, BadVersion,
BadChannelName, UnknownPlatform, MissingField, BadRollout).
Pure sx, depends only on modules/std.sx; lookups left as linear scans over
List (no HashMap). tests/domain_validate.sx asserts valid App/Release/
Artifact/Channel are accepted and each invalid case is rejected with the
exact expected error tag.
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.
