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-album.php

@@ -0,0 +1,50 @@
+<?php
+/**
+ * Album card partial template.
+ *
+ * @package WP_FediStream
+ *
+ * @var array $post Album data array.
+ */
+
+// Prevent direct file access.
+if ( ! defined( 'ABSPATH' ) ) {
+    exit;
+}
+?>
+<article class="fedistream-card fedistream-card--album">
+    <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 else : ?>
+                <div class="fedistream-card__placeholder fedistream-card__placeholder--album">
+                    <svg viewBox="0 0 24 24" fill="currentColor"><path d="M12 2C6.48 2 2 6.48 2 12s4.48 10 10 10 10-4.48 10-10S17.52 2 12 2zm0 14.5c-2.49 0-4.5-2.01-4.5-4.5S9.51 7.5 12 7.5s4.5 2.01 4.5 4.5-2.01 4.5-4.5 4.5zm0-5.5c-.55 0-1 .45-1 1s.45 1 1 1 1-.45 1-1-.45-1-1-1z"/></svg>
+                </div>
+            <?php endif; ?>
+        </div>
+        <div class="fedistream-card__content">
+            <h3 class="fedistream-card__title"><?php echo esc_html( $post['title'] ?? '' ); ?></h3>
+            <?php if ( ! empty( $post['artist_name'] ) ) : ?>
+                <p class="fedistream-card__artist"><?php echo esc_html( $post['artist_name'] ); ?></p>
+            <?php endif; ?>
+            <p class="fedistream-card__meta">
+                <span class="fedistream-card__type"><?php echo esc_html( $post['album_type_label'] ?? '' ); ?></span>
+                <?php if ( ! empty( $post['release_year'] ) ) : ?>
+                    <span class="fedistream-card__year"><?php echo esc_html( $post['release_year'] ); ?></span>
+                <?php endif; ?>
+            </p>
+            <?php if ( ! empty( $post['total_tracks'] ) && $post['total_tracks'] > 0 ) : ?>
+                <p class="fedistream-card__stats">
+                    <?php
+                    printf(
+                        /* translators: %d: number of tracks */
+                        esc_html( _n( '%d track', '%d tracks', $post['total_tracks'], 'wp-fedistream' ) ),
+                        (int) $post['total_tracks']
+                    );
+                    ?>
+                </p>
+            <?php endif; ?>
+        </div>
+    </a>
+</article>