feat: Replace Twig with native PHP templates

- Remove twig/twig dependency from composer.json
- Convert all 25 Twig templates to native PHP templates
- New render() method in Plugin.php using PHP include with output buffering
- New render_partial() helper method for including partials
- Templates support theme overrides via fedistream/ directory
- Reduced plugin size by eliminating Twig and its dependencies

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

templates/partials/card-track.php

@@ -0,0 +1,56 @@
+<?php
+/**
+ * Track card partial template.
+ *
+ * @package WP_FediStream
+ *
+ * @var array $post Track data array.
+ */
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+    exit;
+}
+?>
+<article class="fedistream-card fedistream-card--track">
+    <a href="<?php echo esc_url( $post['permalink'] ?? '' ); ?>" class="fedistream-card__link">
+        <div class="fedistream-card__image fedistream-card__image--square">
+            <?php if ( ! empty( $post['thumbnail'] ) ) : ?>
+                <img src="<?php echo esc_url( $post['thumbnail'] ); ?>" alt="<?php echo esc_attr( $post['title'] ?? '' ); ?>" loading="lazy">
+            <?php elseif ( ! empty( $post['album_artwork'] ) ) : ?>
+                <img src="<?php echo esc_url( $post['album_artwork'] ); ?>" alt="<?php echo esc_attr( $post['title'] ?? '' ); ?>" loading="lazy">
+            <?php else : ?>
+                <div class="fedistream-card__placeholder fedistream-card__placeholder--track">
+                    <svg viewBox="0 0 24 24" fill="currentColor"><path d="M12 3v10.55c-.59-.34-1.27-.55-2-.55-2.21 0-4 1.79-4 4s1.79 4 4 4 4-1.79 4-4V7h4V3h-6z"/></svg>
+                </div>
+            <?php endif; ?>
+            <?php if ( ! empty( $post['explicit'] ) ) : ?>
+                <span class="fedistream-card__badge fedistream-card__badge--explicit">E</span>
+            <?php endif; ?>
+        </div>
+        <div class="fedistream-card__content">
+            <h3 class="fedistream-card__title"><?php echo esc_html( $post['title'] ?? '' ); ?></h3>
+            <?php if ( ! empty( $post['artists'] ) && is_array( $post['artists'] ) ) : ?>
+                <p class="fedistream-card__artist">
+                    <?php
+                    $artist_names = array_map(
+                        function ( $artist ) {
+                            return esc_html( $artist['name'] ?? '' );
+                        },
+                        $post['artists']
+                    );
+                    echo implode( ', ', $artist_names ); // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
+                    ?>
+                </p>
+            <?php endif; ?>
+            <p class="fedistream-card__meta">
+                <?php if ( ! empty( $post['album_title'] ) ) : ?>
+                    <span class="fedistream-card__album"><?php echo esc_html( $post['album_title'] ); ?></span>
+                <?php endif; ?>
+                <?php if ( ! empty( $post['duration_formatted'] ) ) : ?>
+                    <span class="fedistream-card__duration"><?php echo esc_html( $post['duration_formatted'] ); ?></span>
+                <?php endif; ?>
+            </p>
+        </div>
+    </a>
+</article>