fix(reference-source): recognize Kotlin files in imported inventories

Classify .kt and .kts at the source owner so imported entries and historical language summaries preserve Kotlin identity.

Validation: production inventory projection covers Kotlin, Gradle script, Java and backup-suffix controls.

Based on #3224.

Co-authored-by: Aurantium <280805072+Aurantium-47@users.noreply.github.com>

src/domain/referenceSourceClassification.ts

@@ -27,6 +27,8 @@ const CODE_EXTENSIONS = new Set([
   "rs",
   "go",
   "java",
+  "kt",
+  "kts",
   "c",
   "h",
   "cpp",
@@ -54,6 +56,8 @@ const LANGUAGE_BY_EXTENSION = new Map<string, string>([
   ["rs", "Rust"],
   ["go", "Go"],
   ["java", "Java"],
+  ["kt", "Kotlin"],
+  ["kts", "Kotlin"],
   ["c", "C"],
   ["h", "C"],
   ["cpp", "C++"],