wp-init: provision fluent plugins via WP_EXTRA_PLUGINS

gustavoo-portfolio-core refuses to activate without fluentform, fluent-crm
and fluent-smtp, but those were gitignored and not installed by the setup:
any fresh clone ended with the core plugin inactive and the seeder skipped.
They are now part of the default WP_EXTRA_PLUGINS (verified slugs on
WordPress.org), with .env.example, compose default, README and .gitignore
updated to match.

.gitignore

@@ -15,9 +15,6 @@ wp-content/themes/twentytwentythree/
 
 # Default WordPress plugins (not part of project)
 wp-content/plugins/akismet/
-wp-content/plugins/fluentform/
-wp-content/plugins/fluent-crm/
-wp-content/plugins/fluent-smtp/
 wp-content/plugins/redis-cache/
 wp-content/plugins/query-monitor/
 wp-content/plugins/hello.php
@@ -26,10 +23,13 @@ wp-content/plugins/index.php
 # Third-party plugins installed from WordPress.org by docker/wp-init.sh
 # (WP_EXTRA_PLUGINS). They are downloaded on first run and updated in place, so
 # they are not versioned here: committing them would add ~45 MB of code that the
-# setup can fetch on demand.
+# setup can fetch on demand. fluent* are required by gustavoo-portfolio-core.
 wp-content/plugins/post-views-counter/
 wp-content/plugins/seo-by-rank-math/
 wp-content/plugins/google-site-kit/
+wp-content/plugins/fluentform/
+wp-content/plugins/fluent-crm/
+wp-content/plugins/fluent-smtp/
 
 # Redis object cache drop-in (auto-installed by wpcli service)
 wp-content/object-cache.php