Add admin login endpoint

src/main/kotlin/de/ruvnox/tactical/security/PasswordHash.kt

@@ -0,0 +1,28 @@
+package de.ruvnox.tactical.security
+
+import java.security.MessageDigest
+import java.util.Base64
+import javax.crypto.SecretKeyFactory
+import javax.crypto.spec.PBEKeySpec
+
+object PasswordHash {
+    fun verify(password: String, storedHash: String?): Boolean {
+        if (storedHash.isNullOrBlank()) return false
+
+        val parts = storedHash.split("$")
+        if (parts.size != 4) return false
+        if (parts[0] != "pbkdf2_sha256") return false
+
+        val iterations = parts[1].toIntOrNull() ?: return false
+        val salt = runCatching { Base64.getDecoder().decode(parts[2]) }.getOrNull() ?: return false
+        val expected = runCatching { Base64.getDecoder().decode(parts[3]) }.getOrNull() ?: return false
+
+        val spec = PBEKeySpec(password.toCharArray(), salt, iterations, expected.size * 8)
+        val actual = SecretKeyFactory
+            .getInstance("PBKDF2WithHmacSHA256")
+            .generateSecret(spec)
+            .encoded
+
+        return MessageDigest.isEqual(expected, actual)
+    }
+}