Fix docs, add .dockerignore, fix base64url padding, fix typo

- Add .dockerignore to exclude .git, vendor, var, tests, docs, .env
  and other non-build files from Docker context
- Fix broken base64url padding in src/Data/Payload.php: str_pad was
  a no-op because the length argument was always < string length.
  Replaced with correct str_repeat approach
- Fix typo in bin/franken.sh: digtialadapt → digitaladapt
- Add comment to bin/franken.sh noting it's a dev utility
- Remove config/reference.php from git tracking (auto-generated file)
  and add to .gitignore
- Fix readme.md: env.example → example.env (matches actual filename)

src/Data/Payload.php

@@ -16,9 +16,9 @@ final class Payload {
 
     public static function decode(string $base64url): ?Payload {
         /* convert the base64url into json string */
-        $json = base64_decode(str_pad(strtr($base64url, '-_', '+/'),
-            strlen($base64url) % 4, '='
-        ), true);
+        $base64 = strtr($base64url, '-_', '+/');
+        $base64 .= str_repeat('=', (4 - strlen($base64) % 4) % 4);
+        $json = base64_decode($base64, true);
         if ($json) {
             /* convert the json string into real data */
             $data = json_decode($json);