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

tests/tree_sitter_integration.rs

@@ -288,7 +288,7 @@ fn test_type_system_keywords_parse() {
 fn test_any_type_highlights_correctly() {
     // Create a minimal test file with any_type usage
     let test_content = r#"
-concept_comparison SkillLevel {
+definition SkillLevel {
     Novice: { skill: any },
     Expert: { skill: Tier is Expert }
 }