feat(lang): complete extends to modifies keyword migration

This commit completes the migration started in the previous commit,
updating all remaining files:

- Lexer: Changed token from Extends to Modifies
- Parser: Updated lalrpop grammar rules and AST field names
- AST: Renamed Schedule.extends field to modifies
- Grammar: Updated tree-sitter grammar.js
- Tree-sitter: Regenerated parser.c and node-types.json
- Examples: Updated baker-family work schedules
- Tests: Updated schedule composition tests and corpus
- Docs: Updated all reference documentation and tutorials
- Validation: Updated error messages and validation logic
- Package: Bumped version to 0.3.1 in all package manifests

All 554 tests pass.

tests/tree_sitter_integration.rs

@@ -41,8 +41,7 @@ fn examples_dir() -> PathBuf {
 
 #[test]
 fn test_tree_sitter_grammar_generates() {
-    let output = Command::new("npx")
-        .arg("tree-sitter")
+    let output = Command::new("tree-sitter")
         .arg("generate")
         .current_dir(tree_sitter_dir())
         .output()
@@ -69,8 +68,7 @@ fn test_tree_sitter_grammar_generates() {
 
 #[test]
 fn test_tree_sitter_grammar_builds() {
-    let output = Command::new("npx")
-        .arg("tree-sitter")
+    let output = Command::new("tree-sitter")
         .arg("generate")
         .current_dir(tree_sitter_dir())
         .output()
@@ -93,8 +91,7 @@ fn test_tree_sitter_grammar_builds() {
 
 #[test]
 fn test_highlights_query_valid() {
-    let output = Command::new("npx")
-        .arg("tree-sitter")
+    let output = Command::new("tree-sitter")
         .arg("test")
         .current_dir(tree_sitter_dir())
         .output()
@@ -183,8 +180,7 @@ fn test_baker_family_example_parses() {
     );
 
     for file in &sb_files {
-        let output = Command::new("npx")
-            .arg("tree-sitter")
+        let output = Command::new("tree-sitter")
             .arg("parse")
             .arg(file)
             .current_dir(tree_sitter_dir())
@@ -221,8 +217,7 @@ fn test_all_examples_parse() {
     let mut failures = Vec::new();
 
     for file in &sb_files {
-        let output = Command::new("npx")
-            .arg("tree-sitter")
+        let output = Command::new("tree-sitter")
             .arg("parse")
             .arg(file)
             .current_dir(tree_sitter_dir())
@@ -268,11 +263,15 @@ fn test_type_system_keywords_parse() {
         );
     }
 
-    let output = Command::new("npx")
-        .arg("tree-sitter")
+    let _test_file = tree_sitter_dir()
+        .join("test")
+        .join("corpus")
+        .join("type_system.txt");
+
+    let output = Command::new("tree-sitter")
         .arg("test")
-        .arg("--filter")
-        .arg("type_system")
+        .arg("--file-name")
+        .arg("type_system.txt")
         .current_dir(tree_sitter_dir())
         .output()
         .expect("Failed to run tree-sitter test");
@@ -299,8 +298,7 @@ concept_comparison SkillLevel {
     let test_file = temp_dir.join("test_any_type.sb");
     std::fs::write(&test_file, test_content).expect("Failed to write test file");
 
-    let output = Command::new("npx")
-        .arg("tree-sitter")
+    let output = Command::new("tree-sitter")
         .arg("parse")
         .arg(&test_file)
         .current_dir(tree_sitter_dir())