feat(lang): rename concept_comparison to definition (v0.3.2)

Renames the `concept_comparison` keyword to `definition` across the
entire codebase for better readability and conciseness.

Changes:
- Tree-sitter grammar: `concept_comparison` node → `definition`
- Tree-sitter queries: highlights, outline, and indents updated
- Zed extension highlights.scm updated to match
- Lexer: `Token::ConceptComparison` → `Token::Definition`
- Parser: `ConceptComparisonDecl` rule → `DefinitionDecl`
- AST: `Declaration::ConceptComparison` → `Declaration::Definition`,
  `ConceptComparisonDecl` struct → `DefinitionDecl`
- All Rust source files updated (validate, names, convert, references,
  semantic_tokens, symbols, code_actions, hover, completion)
- `validate_concept_comparison_patterns` → `validate_definition_patterns`
- Example file and test corpus updated
- Spec docs: created SBIR-v0.3.2-SPEC.md, updated TYPE-SYSTEM.md,
  README.md, SBIR-CHANGELOG.md, SBIR-v0.3.1-SPEC.md

tree-sitter-storybook/test/corpus/type_system.txt

@@ -58,10 +58,10 @@ sub_concept BakedGood.Quality {
           value: (float))))))
 
 ==================
-Concept comparison
+Definition
 ==================
 
-concept_comparison SkillLevel {
+definition SkillLevel {
     Apprentice: { freshness: any },
     Master: { freshness: Tier is Master }
 }
@@ -70,7 +70,7 @@ concept_comparison SkillLevel {
 
 (source_file
   (declaration
-    (concept_comparison
+    (definition
       name: (identifier)
       (variant_pattern
         name: (identifier)