feat: enable .isc loading via Interscript.transliterate()

Interscript.locate now searches for .isc files (preferred) alongside
.iml and .imp. Compiler.call detects the file extension and dispatches
to the ISC parser + NodeAdapter for .isc files, or DSL.parse for .imp.

This makes ISC a first-class source format: users can call
Interscript.transliterate("foo") and it will use foo.isc if present,
falling back to foo.imp.

Verified: identical transliteration output from .isc and .imp.

Author: ronaldtse

lib/interscript.rb

@@ -31,8 +31,8 @@ def locate map_name
       map_name = map_aliases[map_name] if map_aliases.include? map_name
 
       load_path.each do |i|
-        # iml is an extension for a library, imp for a map
-        ["iml", "imp"].each do |ext|
+        # isc: new ISC format, iml: library, imp: legacy Ruby DSL
+        ["isc", "iml", "imp"].each do |ext|
           f = File.expand_path("#{map_name}.#{ext}", i)
           return f if File.exist?(f)
         end

lib/interscript/compiler.rb

@@ -10,13 +10,28 @@ class Interscript::Compiler
 
   def self.call(map, **kwargs)
     if String === map
-      map = Interscript::DSL.parse(map)
+      path = Interscript.locate(map) rescue nil
+      map = if path&.end_with?(".isc")
+              parse_isc(path)
+            else
+              Interscript::DSL.parse(map)
+            end
     end
     compiler = new
     compiler.compile(map, **kwargs)
     compiler
   end
 
+  # Parse an ISC source file into an Interscript::Node::Document.
+  # This bridges the new ISC format to the existing runtime.
+  def self.parse_isc(path)
+    source = File.read(path, encoding: "UTF-8")
+    filename = File.basename(path)
+    tree = Interscript::Isc::Parser.parse(source, filename: filename)
+    doc = Interscript::Isc::DocumentBuilder.build(tree, filename: filename)
+    Interscript::Isc::NodeAdapter.to_interscript_node(doc)
+  end
+
   def compile(map)
     raise NotImplementedError, "Compile method on #{self.class} is not implemented"
   end