Phase 0: strip JetBrains template, register Jai language and file type

- delete demo tool window + message bundle, rewrite plugin.xml metadata
- add JaiLanguage, JaiFileType, file icon, JaiTokenTypes (from the compiler's
  own lexer: modules/Jai_Lexer/module.jai)
- add ./jaitest: runs tests and reports the JUnit XML, not just the exit code
- ignore .kotlin

src/test/kotlin/dev/hgh/jai/JaiFileTypeTest.kt

@@ -0,0 +1,25 @@
+package dev.hgh.jai
+
+import com.intellij.openapi.fileTypes.FileTypeManager
+import com.intellij.testFramework.fixtures.BasePlatformTestCase
+
+/**
+ * Verifies plugin.xml wiring: the `.jai` extension resolves to our file type and
+ * our language, without launching an IDE.
+ */
+class JaiFileTypeTest : BasePlatformTestCase() {
+    fun testJaiExtensionIsRegistered() {
+        val type = FileTypeManager.getInstance().getFileTypeByExtension("jai")
+        assertEquals(JaiFileType, type)
+    }
+
+    /**
+     * The *virtual* file already resolves to our type. The PSI file's language stays
+     * plain text until a ParserDefinition is registered (phase 3) — asserting that here
+     * would be asserting the platform's fallback, not our wiring.
+     */
+    fun testVirtualFileUsesJaiFileType() {
+        val file = myFixture.configureByText("sample.jai", "main :: () { }")
+        assertEquals(JaiFileType, file.virtualFile.fileType)
+    }
+}