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

crates/g3-core/examples/test_code/Example.kt

@@ -1,24 +0,0 @@
-package com.example
-
-class Person(val name: String, val age: Int) {
-    fun greet() {
-        println("Hello, I'm $name")
-    }
-    
-    fun getAge(): Int {
-        return age
-    }
-}
-
-interface Greeter {
-    fun sayHello()
-}
-
-fun main() {
-    val person = Person("Alice", 30)
-    person.greet()
-}
-
-fun add(a: Int, b: Int): Int {
-    return a + b
-}

crates/g3-core/examples/test_code/example.rkt

@@ -1,24 +0,0 @@
-#lang racket
-
-(define (greet name)
-  (printf "Hello, ~a!\n" name))
-
-(define (add x y)
-  (+ x y))
-
-(define (factorial n)
-  (if (<= n 1)
-      1
-      (* n (factorial (- n 1)))))
-
-(struct person (name age) #:transparent)
-
-(define (person-greet p)
-  (printf "Hello, I'm ~a\n" (person-name p)))
-
-(greet "World")
-(displayln (add 5 3))
-(displayln (factorial 5))
-
-(define alice (person "Alice" 30))
-(person-greet alice)