Step 17b: Pretext — DOM-free text layout with otfm font measurement

Pure SX text layout library with one IO boundary (text-measure perform).
Knuth-Plass optimal line breaking, Liang's hyphenation, position calculation.

Library (lib/text-layout.sx):
- break-lines: Knuth-Plass DP over word widths
- break-lines-greedy: simple word-wrap for comparison
- hyphenate-word: Liang's trie algorithm
- position-line/position-lines: running x/y sums
- measure-text: single perform (text-measure IO)

Server font measurement (otfm):
- Reads OpenType cmap + hmtx tables from .ttf files
- DejaVu Serif/Sans bundled in shared/static/fonts/
- _cek_io_resolver hook: perform works inside aser/eval_expr
- JIT VM suspension inline resolution for IO in compiled code

~font component (shared/sx/templates/font.sx):
- Works like ~tw: emits @font-face CSS via cssx scope
- Sets font-family on parent via spread
- Deduplicates font declarations

Infrastructure fixes:
- stdin load command: per-expression error handling (was aborting on first error)
- cek_run IO hook: _cek_io_resolver in sx_types.ml
- JIT VmSuspended: inline IO resolution when resolver installed
- ListRef handling in IO resolver (perform creates ListRef, not List)

Demo page at /sx/(applications.(pretext)):
- Hero: justified paragraph with otfm-measured proportional widths
- Greedy vs Knuth-Plass side-by-side comparison
- Badness scoring visualization
- Hyphenation syllable decomposition

25 new tests (spec/tests/test-text-layout.sx), 3201/3201 passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/run_tests.ml

@@ -1422,6 +1422,7 @@ let run_spec_tests env test_files =
   let templates_dir = Filename.concat project_dir "shared/sx/templates" in
   load_module "tw.sx" templates_dir;
   load_module "tw-layout.sx" templates_dir;
+  load_module "font.sx" templates_dir;
   load_module "tw-type.sx" templates_dir;
   (* SX docs site: components, handlers, demos *)
   let sx_comp_dir = Filename.concat project_dir "sx/sxc" in