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

src/lsp/completion_tests.rs

@@ -269,8 +269,8 @@ character Bob {}"#;
                         "Should have sub_concept keyword"
                     );
                     assert!(
-                        items.iter().any(|item| item.label == "concept_comparison"),
-                        "Should have concept_comparison keyword"
+                        items.iter().any(|item| item.label == "definition"),
+                        "Should have definition keyword"
                     );
 
                     // Check snippets have correct format