fix: require a compiled artifact for entrypoints.jobs

Module discovery gated the compiled-ESM rule on an allowlist,
`["schema", "server", "ui"]`, so `entrypoints.jobs` accepted
`./src/jobs/index.ts`. Every other executable entrypoint required a built
`.js` or `.mjs`; `jobs` did not, purely because it was never added to
that list. It is the second entrypoint to slip through the same way —
`ui` did too, until Phase 6A added it explicitly — which is the argument
against the allowlist rather than against `jobs`.

The rule is now expressed as "every entrypoint except a directory
entrypoint", with `migrations` the only member of that set. A new
manifest entrypoint therefore defaults to the stricter validation instead
of silently escaping it. The same constant replaces the two existing
`=== "migrations"` special cases for the file/directory kind check and
its message, so the one thing that distinguishes `migrations` is stated
once. The directory message is now templated and produces byte-identical
text.

Every other entrypoint guarantee is untouched: package-relative paths,
no traversal, inside-package before and after symlink resolution, the
artifact must exist, and it must be a file.

No runtime was added. `entrypoints.jobs` still has no consumer — it is
declared, validated, and never executed — exactly as it has been since
ADR 0006, and as `ui` was before its host loader existed. The manifest
schema is unchanged and this stays within v4: the field, its type, and
its optionality are all the same, and only discovery's validation of the
declared path tightened.

Compatibility impact is nil in first-party code: no module, template, or
fixture declares a `jobs` entrypoint at all. A third-party module
declaring a source-TypeScript path would now fail discovery, which is the
intended correction.

Tests cover accepted `.js` and `.mjs`, rejected `.ts`/`.tsx`/`.cjs`, a
missing artifact, a directory, a symlink escaping the package, and that
discovery still never evaluates the artifact. The three rejection cases
were confirmed to fail against the previous implementation.

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/architecture/decisions/0023-module-ui-build-pipeline.md

@@ -198,3 +198,9 @@ loading; and every real feature module. `entrypoints.jobs` still accepts source
 other executable entrypoints require compiled output; this pass reused the *path* grammar from
 `@ekklesia/contracts` but did not centralize the *extension* rule, so that inconsistency is
 unchanged and still open.
+
+> **Correction — this deferred item is closed.** `entrypoints.jobs` now requires a compiled `.js` or
+> `.mjs` artifact, exactly like `server`, `schema`, and `ui`. Module discovery expresses the rule as
+> "every entrypoint except the directory entrypoint (`migrations`)", so the omission that let `jobs`
+> escape it cannot recur. No jobs runtime was added: the entrypoint is still declared, validated, and
+> never executed. Every other item in this list remains deferred.