sx: step 11 — migrate prolog hook + add worker plugin

Move `hs-prolog-hook` / `hs-set-prolog-hook!` / `prolog` out of
`lib/hyperscript/runtime.sx` into a self-contained plugin file at
`lib/hyperscript/plugins/prolog.sx`. The API surface is preserved —
`lib/prolog/hs-bridge.sx::pl-install-hs-hook!` still calls
`hs-set-prolog-hook!` exactly as before, just resolved to the plugin
file's binding rather than runtime.sx's.

Move the E39 worker stub registration out of `lib/hyperscript/parser.sx`
into `lib/hyperscript/plugins/worker.sx`. The plugin calls
`(hs-register-feature! "worker" ...)` at file load time. Behaviour is
identical — `worker MyWorker ...` raises the same helpful "plugin not
installed" error, just routed through the registry from a separate
file. The pre-existing `behavioral` test for the helpful error
("raises a helpful error when the worker plugin is not installed")
still passes via the new path.

Wire-up:
- OCaml `bin/run_tests.ml`: load `plugins/worker.sx` and
  `plugins/prolog.sx` after `runtime.sx`, before `integration.sx`.
- JS `tests/hs-kernel-eval.js`: extend HS module list with
  `hs-worker` / `hs-prolog`; add `HS_PLUGINS` resolver branch so the
  `hs-` prefix maps to `lib/hyperscript/plugins/`.
- WASM `hosts/ocaml/browser/bundle.sh`: copy plugin files into
  `dist/sx/hs-<name>.sx`.
- WASM `hosts/ocaml/browser/compile-modules.js`: add `hs-worker` /
  `hs-prolog` to `FILES`, `HS_DEPS`, and `HS_LAZY` so the lazy loader
  resolves them on first reference.
- Worker plugin carries a sentinel `(define hs-worker-loaded? true)`
  so `extractDefines` indexes it in the module manifest (the lazy
  loader skips files with no defines).

Mirrors `shared/static/wasm/sx/hs-{parser,runtime}.sx` are byte-identical
to source; new mirrors `hs-{prolog,worker}.sx` written via sx_write_file.

OCaml: 4545 passed, 1339 failed — matches baseline.
JS: 2591 passed, 2465 failed — matches baseline.
Smoke tests: `(prolog ...)` raises "prolog hook not installed" cleanly,
`(hs-set-prolog-hook! ...)` then `(prolog ...)` returns the hook result,
`(hs-compile "worker MyWorker def noop() end end")` raises the worker
stub error via the registry path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plans/sx-improvements.md

@@ -217,7 +217,7 @@ these when operands are known numbers/lists.
 | 8 — exhaustiveness warnings | [x] | 6d391119 |
 | 9 — parser feature registry | [x] | 986d6411 |
 | 10 — compiler + as converter registry | [x] | d22361e4 |
-| 11 — plugin migration + worker | [ ] | — |
+| 11 — plugin migration + worker | [x] | (pending) |
 | 12 — frame records | [ ] | — |
 | 13 — buffer primitive | [ ] | — |
 | 14 — inline primitives JIT | [ ] | — |