fix: Complete memory leak fix with shortcode context tracking

The v0.4.1 fix was incomplete - shortcodes called get_*_data() methods
directly, bypassing the recursion tracking in get_post_data().

Changes:
- Added $in_shortcode_context flag to TemplateLoader
- Added enter/exit_shortcode_context() methods
- All shortcode render methods now enter context before data loading
- When in shortcode context, the_content filter is always skipped

This fully prevents infinite recursion when post content contains
FediStream shortcodes that would otherwise recursively render.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

wp-fedistream.php

@@ -3,7 +3,7 @@
  * Plugin Name: WP FediStream
  * Plugin URI: https://src.bundespruefstelle.ch/magdev/wp-fedistream
  * Description: Stream music over ActivityPub - Build your own music streaming platform for Musicians and Labels.
- * Version: 0.4.1
+ * Version: 0.4.2
  * Requires at least: 6.4
  * Requires PHP: 8.3
  * Author: Marco Graetsch
@@ -26,7 +26,7 @@ if ( ! defined( 'ABSPATH' ) ) {
  *
  * @var string
  */
-define( 'WP_FEDISTREAM_VERSION', '0.4.1' );
+define( 'WP_FEDISTREAM_VERSION', '0.4.2' );
 
 /**
  * Plugin file path.