feat(resolver): implement cross-file template resolution

Enable characters to inherit from templates defined in different files
across the project structure.

- Add file_index field to NameEntry to track declaration source files
- Update NameTable::from_files() to set file indices when merging tables
- Change conversion pipeline to pass &[ast::File] instead of flat arrays
- Update merge functions to use two-level indexing:
  all_files[entry.file_index].declarations[entry.decl_index]
- Update all affected tests to use new signatures

src/resolve/convert_prop_tests.rs

@@ -89,9 +89,9 @@ fn valid_unique_fields() -> impl Strategy<Value = Vec<Field>> {
 fn valid_character() -> impl Strategy<Value = Character> {
     (valid_ident(), valid_unique_fields()).prop_map(|(name, fields)| Character {
         name,
+        species: None,
         fields,
         template: None,
-
         span: Span::new(0, 100),
     })
 }
@@ -192,7 +192,8 @@ proptest! {
         val2 in valid_value()
     ) {
         let character = Character {
-            name,
+            name: name.clone(),
+            species: None,
             fields: vec![
                 Field {
                     name: field_name.clone(),
@@ -239,6 +240,7 @@ proptest! {
     fn test_empty_character_converts(name in valid_ident()) {
         let character = Character {
             name: name.clone(),
+            species: None,
             fields: vec![],
             template: None,
 
@@ -268,7 +270,7 @@ proptest! {
 
     #[test]
     fn test_file_with_use_declarations_skips_them(
-        characters in prop::collection::vec(valid_character(), 1..5),
+        char_count in 1usize..5,
         use_count in 0usize..5
     ) {
         let mut declarations = vec![];
@@ -282,9 +284,16 @@ proptest! {
             }));
         }
 
-        // Add characters
-        let char_count = characters.len();
-        declarations.extend(characters.into_iter().map(Declaration::Character));
+        // Add characters with unique names to avoid duplicate definition errors
+        for i in 0..char_count {
+            declarations.push(Declaration::Character(Character {
+                name: format!("Char{}", i),
+                species: None,
+                fields: vec![],
+                template: None,
+                span: Span::new(0, 100),
+            }));
+        }
 
         let file = File { declarations };
         let resolved = convert_file(&file).unwrap();
@@ -308,6 +317,7 @@ mod edge_cases {
         ) {
             let character = Character {
                 name: "Test".to_string(),
+            species: None,
                 fields: vec![
                     Field {
                         name: "int_field".to_string(),
@@ -351,6 +361,7 @@ mod edge_cases {
         ) {
             let character = Character {
                 name: name.clone(),
+            species: None,
                 fields: vec![Field {
                     name: field_name.clone(),
                     value: Value::String(string_val.clone()),