Move plugins to manifest, pin Docker version, add Makefile

- Add plugins.txt listing all plugins for reproducible installs
- Add Makefile with setup/start/stop/install-plugins targets
- Remove user/plugins/ from git tracking
- Pin Docker image to 1.7.49.5-ls244

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/email/vendor/symfony/polyfill-php80/README.md

@@ -1,25 +0,0 @@
-Symfony Polyfill / Php80
-========================
-
-This component provides features added to PHP 8.0 core:
-
-- [`Stringable`](https://php.net/stringable) interface
-- [`fdiv`](https://php.net/fdiv)
-- [`ValueError`](https://php.net/valueerror) class
-- [`UnhandledMatchError`](https://php.net/unhandledmatcherror) class
-- `FILTER_VALIDATE_BOOL` constant
-- [`get_debug_type`](https://php.net/get_debug_type)
-- [`PhpToken`](https://php.net/phptoken) class
-- [`preg_last_error_msg`](https://php.net/preg_last_error_msg)
-- [`str_contains`](https://php.net/str_contains)
-- [`str_starts_with`](https://php.net/str_starts_with)
-- [`str_ends_with`](https://php.net/str_ends_with)
-- [`get_resource_id`](https://php.net/get_resource_id)
-
-More information can be found in the
-[main Polyfill README](https://github.com/symfony/polyfill/blob/main/README.md).
-
-License
-=======
-
-This library is released under the [MIT license](LICENSE).