Refactor MCP tree server: dispatch table, caching, validation, subprocess cleanup

Break up the 1735-line handle_tool match into 45 individual handler functions
with hashtable-based dispatch. Add mtime-based file parse caching (AST + CST),
consolidated run_command helper replacing 9 bare open_process_in patterns,
require_file/require_dir input validation, and pagination (limit/offset) for
sx_find_across, sx_comp_list, sx_comp_usage. Also includes pending VM changes:
rest-arity support, hyperscript parser, compiler/transpiler updates.

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

hosts/ocaml/transpiler.sx

@@ -269,7 +269,8 @@
     "try-catch"
     "set-render-active!"
     "scope-emitted"
-    "jit-try-call"))
+    "jit-try-call"
+    "jit-skip?"))
 
 (define
   ml-is-known-name?