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

examples/baker-family/schema/types.sb

@@ -33,9 +33,9 @@ sub_concept SkillLevel.Tier {
     Master
 }
 
-// Concept comparison - compile-time mapping of skill tiers to quality expectations
+// Definition - compile-time mapping of skill tiers to quality expectations
 // An Apprentice can produce any quality; a Master must produce fresh goods
-concept_comparison SkillLevel {
+definition SkillLevel {
     Apprentice: {
         baking_skill: Tier is Apprentice,
         freshness: any