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.

src/error_showcase_tests.rs

@@ -319,7 +319,7 @@ fn test_trait_out_of_range_negative() {
 fn test_schedule_overlap_error() {
     let schedule = Schedule {
         name: "DailyRoutine".to_string(),
-        extends: None,
+        modifies: None,
         fields: Vec::new(),
         recurrences: Vec::new(),
         blocks: vec![

src/resolve/validate.rs

@@ -373,20 +373,20 @@ pub fn validate_institution_resource_links(
 /// Validate schedule composition requirements
 ///
 /// Checks:
-/// 1. All blocks in extended schedules have names
+/// 1. All blocks in modified schedules have names
 /// 2. Override blocks reference valid block names (requires name resolution)
 pub fn validate_schedule_composition(schedule: &Schedule, collector: &mut ErrorCollector) {
-    // If schedule extends another, all blocks must have names for override system
-    if schedule.extends.is_some() {
+    // If schedule modifies another, all blocks must have names for override system
+    if schedule.modifies.is_some() {
         for block in &schedule.blocks {
             if block.name.is_none() && !block.activity.is_empty() {
                 collector.add(ResolveError::ValidationError {
                     message: format!(
-                        "Schedule '{}' extends another schedule but has unnamed blocks",
+                        "Schedule '{}' modifies another schedule but has unnamed blocks",
                         schedule.name
                     ),
                     help: Some(
-                        "When a schedule extends another, all blocks must have names to support the override system. Use 'block name { ... }' syntax instead of 'time -> time : activity { ... }'.".to_string()
+                        "When a schedule modifies another, all blocks must have names to support the override system. Use 'block name { ... }' syntax instead of 'time -> time : activity { ... }'.".to_string()
                     ),
                 });
             }

src/syntax/ast.rs

@@ -249,7 +249,7 @@ pub struct Transition {
 #[derive(Debug, Clone, PartialEq)]
 pub struct Schedule {
     pub name: String,
-    pub extends: Option<String>, // Base schedule to extend
+    pub modifies: Option<String>, // Base schedule to modify
     pub blocks: Vec<ScheduleBlock>,
     pub recurrences: Vec<RecurrencePattern>, // Recurring events
     pub fields: Vec<Field>,                  // Documentation prose blocks, metadata

src/syntax/lexer.rs

@@ -87,8 +87,8 @@ pub enum Token {
     Tree,
     #[token("priority")]
     Priority,
-    #[token("extends")]
-    Extends,
+    #[token("modifies")]
+    Modifies,
     #[token("override")]
     Override,
     #[token("recurrence")]

src/syntax/parser.lalrpop

@@ -386,16 +386,16 @@ Schedule: Schedule = {
     // Simple schedule: schedule Name { ... }
     <start:@L> "schedule" <name:Ident> "{" <body:ScheduleBody> "}" <end:@R> => Schedule {
         name,
-        extends: None,
+        modifies: None,
         fields: body.0,
         blocks: body.1,
         recurrences: body.2,
         span: Span::new(start, end),
     },
-    // Extending schedule: schedule Name extends Base { ... }
-    <start:@L> "schedule" <name:Ident> "extends" <base:Ident> "{" <body:ScheduleBody> "}" <end:@R> => Schedule {
+    // Modifying schedule: schedule Name modifies Base { ... }
+    <start:@L> "schedule" <name:Ident> "modifies" <base:Ident> "{" <body:ScheduleBody> "}" <end:@R> => Schedule {
         name,
-        extends: Some(base),
+        modifies: Some(base),
         fields: body.0,
         blocks: body.1,
         recurrences: body.2,
@@ -1003,7 +1003,7 @@ extern {
         "schedules" => Token::Schedules,
         "tree" => Token::Tree,
         "priority" => Token::Priority,
-        "extends" => Token::Extends,
+        "modifies" => Token::Modifies,
         "override" => Token::Override,
         "recurrence" => Token::Recurrence,
         "season" => Token::Season,

src/syntax/schedule_composition_tests.rs

@@ -29,7 +29,7 @@ schedule DailyRoutine {
     match &file.declarations[0] {
         | Declaration::Schedule(s) => {
             assert_eq!(s.name, "DailyRoutine");
-            assert!(s.extends.is_none());
+            assert!(s.modifies.is_none());
             assert_eq!(s.blocks.len(), 2);
             assert_eq!(s.recurrences.len(), 0);
 
@@ -43,9 +43,9 @@ schedule DailyRoutine {
 }
 
 #[test]
-fn test_schedule_extends() {
+fn test_schedule_modifies() {
     let input = r#"
-schedule BakerSchedule extends BaseWorkday {
+schedule BakerSchedule modifies BaseWorkday {
     block work { 05:00 -> 13:00, action: BakingWork }
 }
 "#;
@@ -60,7 +60,7 @@ schedule BakerSchedule extends BaseWorkday {
     match &file.declarations[0] {
         | Declaration::Schedule(s) => {
             assert_eq!(s.name, "BakerSchedule");
-            assert_eq!(s.extends, Some("BaseWorkday".to_string()));
+            assert_eq!(s.modifies, Some("BaseWorkday".to_string()));
         },
         | _ => panic!("Expected Schedule declaration"),
     }
@@ -104,7 +104,7 @@ schedule WorkSchedule {
 #[test]
 fn test_override_block() {
     let input = r#"
-schedule BakerSchedule extends BaseWorkday {
+schedule BakerSchedule modifies BaseWorkday {
     override work { 05:00 -> 13:00, action: BakingWork }
     block prep { 03:00 -> 05:00, action: PrepBread }
 }
@@ -208,7 +208,7 @@ schedule WorkSchedule {
 #[test]
 fn test_mixed_blocks_and_recurrences() {
     let input = r#"
-schedule CompleteSchedule extends BaseSchedule {
+schedule CompleteSchedule modifies BaseSchedule {
     block morning { 06:00 -> 12:00, action: MorningRoutine }
 
     recurrence Weekend on Spiritday {
@@ -229,7 +229,7 @@ schedule CompleteSchedule extends BaseSchedule {
     match &file.declarations[0] {
         | Declaration::Schedule(s) => {
             assert_eq!(s.name, "CompleteSchedule");
-            assert_eq!(s.extends, Some("BaseSchedule".to_string()));
+            assert_eq!(s.modifies, Some("BaseSchedule".to_string()));
             assert_eq!(s.blocks.len(), 2); // morning and override evening
             assert_eq!(s.recurrences.len(), 1); // Weekend