feat: ship Peptide Reconstitution Calculator v1.0.0

Interactive reconstitution calculator with peptide-specific presets.

Core features:
- [prc_calculator] shortcode with instant client-side math
- Concentration (mg/mL), mcg/unit, injection volume, syringe units, doses/vial
- Live presets from PR Core dosing data (graceful fallback to 8 defaults)
- REST API (prc/v1): presets list/detail + server-side calculate
- Transient-cached presets with event-driven invalidation
- Dark mode + responsive design (320px+)
- Full teardown in uninstall.php

12 PHP files (max 241 lines), 1 JS file, 1 CSS file.
CI: PHP lint 8.1-8.3, PHPCS WordPress, 300-line check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

includes/class-prc-deactivator.php

@@ -0,0 +1,27 @@
+<?php
+/**
+ * Deactivation handler.
+ *
+ * What: Runs on plugin deactivation — flushes rewrite rules.
+ * Who calls it: register_deactivation_hook in bootstrap.
+ * Dependencies: None.
+ */
+
+declare(strict_types=1);
+
+/**
+ * Handles plugin deactivation tasks.
+ */
+class PRC_Deactivator {
+
+	/**
+	 * Run deactivation tasks.
+	 *
+	 * Flushes rewrite rules to remove any routes this plugin registered.
+	 *
+	 * @return void
+	 */
+	public static function deactivate(): void {
+		flush_rewrite_rules();
+	}
+}