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/router.sx

@@ -17,6 +17,47 @@
 ;; "/" → ()
 ;; "/docs/" → ("docs")
 
+
+(define-library (web router)
+  (export
+    split-path-segments
+    make-route-segment
+    parse-route-pattern
+    match-route-segments
+    match-route
+    find-matching-route
+    _fn-to-segment
+    sx-url-to-path
+    _count-leading-dots
+    _strip-trailing-close
+    _index-of-safe
+    _last-index-of
+    _pop-sx-url-level
+    _pop-sx-url-levels
+    _split-pos-kw
+    _parse-relative-body
+    _extract-innermost
+    _find-kw-in-tokens
+    _find-keyword-value
+    _replace-kw-in-tokens
+    _set-keyword-in-content
+    _is-delta-value?
+    _apply-delta
+    _apply-kw-pairs
+    _apply-keywords-to-url
+    _normalize-relative
+    resolve-relative-url
+    relative-sx-url?
+    _url-special-forms
+    url-special-form?
+    parse-sx-url
+    url-special-form-name
+    url-special-form-inner
+    url-to-expr
+    auto-quote-unknowns
+    prepare-url-expr)
+  (begin
+
 (define split-path-segments :effects []
   (fn ((path :as string))
     (let ((trimmed (if (starts-with? path "/") (slice path 1) path)))
@@ -678,3 +719,9 @@
 ;;
 ;; From parser.sx: sx-parse, sx-serialize
 ;; --------------------------------------------------------------------------
+
+
+)) ;; end define-library
+
+;; Re-export to global namespace for backward compatibility
+(import (web router))