Add Racket tree-sitter support, remove Kotlin

- Add tree-sitter-racket dependency (v0.24)
- Initialize Racket parser in code search
- Add .rkt, .rktl, .rktd file extensions
- Add test_racket_search test
- Remove Kotlin from supported languages (was disabled)
- Clean up duplicate test files

Supported languages: Rust, Python, JavaScript, TypeScript, Go, Java, C, C++, Racket

Cargo.lock

@@ -1453,6 +1453,7 @@ dependencies = [
  "tree-sitter-java",
  "tree-sitter-javascript",
  "tree-sitter-python",
+ "tree-sitter-racket",
  "tree-sitter-rust",
  "tree-sitter-scheme",
  "tree-sitter-typescript",
@@ -3946,6 +3947,16 @@ dependencies = [
  "tree-sitter-language",
 ]
 
+[[package]]
+name = "tree-sitter-racket"
+version = "0.24.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8395b6a054e6264c67e1ef915f239c4f86575b7d7c69638bdbf3c336c58f128"
+dependencies = [
+ "cc",
+ "tree-sitter-language",
+]
+
 [[package]]
 name = "tree-sitter-rust"
 version = "0.23.3"