feat: verification scanner + admin UI (PR Core v0.4.0)

Implements recurring verification scanner, dashboard widget, per-post sidebar meta box, reader-facing last-verified display, and unified settings panel. Bumps to v0.4.0.

Co-authored-by: peptiderepo <peptiderepo@users.noreply.github.com>

includes/frontend/class-pr-core-verification-display.php

@@ -0,0 +1,81 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Frontend verification date display on peptide single pages.
+ *
+ * What: Appends last-verified date after verdict card on reader-facing pages.
+ * Who calls it: PR_Core::init() hooks the_content filter.
+ * Dependencies: None (hooked via the_content).
+ *
+ * @see includes/class-pr-core.php — Registers the_content hook.
+ */
+class PR_Core_Verification_Display {
+
+	/**
+	 * Initialize frontend hooks.
+	 *
+	 * Side effects: Registers the_content filter.
+	 *
+	 * @return void
+	 */
+	public static function init(): void {
+		add_filter( 'the_content', [ __CLASS__, 'append_verification_display' ], 20 );
+	}
+
+	/**
+	 * Append verification display after verdict card.
+	 *
+	 * @param string $content The post content.
+	 * @return string Modified content.
+	 */
+	public static function append_verification_display( string $content ): string {
+		// Only on peptide CPT, not in admin.
+		if ( is_admin() || ! is_singular( PR_Core_Peptide_CPT::POST_TYPE ) ) {
+			return $content;
+		}
+
+		$post_id = get_the_ID();
+		if ( ! $post_id ) {
+			return $content;
+		}
+
+		// Only if _pr_last_source_verified is set.
+		$last_verified = get_post_meta( $post_id, '_pr_last_source_verified', true );
+		if ( empty( $last_verified ) ) {
+			return $content;
+		}
+
+		// Find the verdict card closing div and append after it.
+		$verdict_close = '</div><!-- .pr-verdict -->';
+		if ( strpos( $content, $verdict_close ) !== false ) {
+			$display = self::render_verification_block( $last_verified );
+			$content = str_replace( $verdict_close, $verdict_close . $display, $content );
+		}
+
+		return $content;
+	}
+
+	/**
+	 * Render the verification block HTML.
+	 *
+	 * @param string $last_verified ISO date string.
+	 * @return string HTML block.
+	 */
+	private static function render_verification_block( string $last_verified ): string {
+		$date_obj = new \DateTime( $last_verified );
+		$formatted_date = $date_obj->format( get_option( 'date_format' ) );
+
+		$html = '<p class="pr-verification-date">';
+		$html .= esc_html__( 'Last verified: ', 'peptide-repo-core' );
+		$html .= sprintf(
+			'<time datetime="%s">%s</time>',
+			esc_attr( $date_obj->format( 'Y-m-d' ) ),
+			esc_html( $formatted_date )
+		);
+		$html .= ' — <a href="' . esc_url( home_url( '/our-methodology/' ) ) . '">' . esc_html__( 'methodology', 'peptide-repo-core' ) . '</a>';
+		$html .= '</p>';
+
+		return $html;
+	}
+}