Step 5 piece 6: migrate 23 .sx files to define-library/import

Wraps all core .sx files in R7RS define-library with explicit export
lists, plus (import ...) at end for backward-compatible global re-export.

Libraries registered:
  (sx bytecode)      — 83 opcode constants
  (sx render)        — 15 tag registries + render helpers
  (sx signals)       — 23 reactive signal primitives
  (sx r7rs)          — 21 R7RS aliases
  (sx compiler)      — 42 compiler functions
  (sx vm)            — 32 VM functions
  (sx freeze)        — 9 freeze/thaw functions
  (sx content)       — 6 content store functions
  (sx callcc)        — 1 call/cc wrapper
  (sx highlight)     — 13 syntax highlighting functions
  (sx stdlib)        — 47 stdlib functions
  (sx swap)          — 13 swap algebra functions
  (sx render-trace)  — 8 render trace functions
  (sx harness)       — 21 test harness functions
  (sx canonical)     — 12 canonical serialization functions
  (web adapter-html) — 13 HTML renderer functions
  (web adapter-sx)   — 13 SX wire format functions
  (web engine)       — 33 hypermedia engine functions
  (web request-handler) — 4 request handling functions
  (web page-helpers) — 12 page helper functions
  (web router)       — 36 routing functions
  (web deps)         — 19 dependency analysis functions
  (web orchestration) — 59 page orchestration functions

Key changes:
- define-library now inherits parent env (env-extend env instead of
  env-extend make-env) so library bodies can access platform primitives
- sx_server.ml: added resolve_library_path + load_library_file for
  import resolution (maps library specs to file paths)
- cek_run_with_io: handles "import" locally instead of sending to
  Python bridge

2608/2608 tests passing.

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

web/engine.sx

@@ -1,3 +1,42 @@
+
+
+(define-library (web engine)
+  (export
+    ENGINE_VERBS
+    DEFAULT_SWAP
+    parse-time
+    parse-trigger-spec
+    default-trigger
+    get-verb-info
+    build-request-headers
+    process-response-headers
+    parse-swap-spec
+    parse-retry-spec
+    next-retry-ms
+    filter-params
+    resolve-target
+    apply-optimistic
+    revert-optimistic
+    find-oob-swaps
+    morph-node
+    sync-attrs
+    morph-children
+    morph-island-children
+    morph-marsh
+    process-signal-updates
+    swap-dom-nodes
+    insert-remaining-siblings
+    swap-html-string
+    handle-history
+    PRELOAD_TTL
+    preload-cache-get
+    preload-cache-set
+    classify-trigger
+    should-boost-link?
+    should-boost-form?
+    parse-sse-swap)
+  (begin
+
 (define ENGINE_VERBS (list "get" "post" "put" "delete" "patch"))
 
 (define DEFAULT_SWAP "outerHTML")
@@ -806,3 +845,9 @@
   parse-sse-swap
   :effects (io)
   (fn (el) (or (dom-get-attr el "sx-sse-swap") "message")))
+
+
+)) ;; end define-library
+
+;; Re-export to global namespace for backward compatibility
+(import (web engine))