feat: add cost/token tracking, monthly budget system, and dry-run mode

- Create PSA_Cost_Tracker class with database table for API call logging
- Log prompt/completion tokens and estimated cost for every OpenRouter API call
- Implement monthly budget system with hard stop (budget of 0 = unlimited)
- Add budget checks in validate_peptide_name() and generate_peptide_content()
- Add dry_run() method to estimate costs before making API calls
- Display monthly usage summary and recent API logs in admin settings
- Add monthly_budget setting to admin interface with number input field
- Update uninstall.php to drop psa_api_logs table on plugin removal

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

uninstall.php

@@ -0,0 +1,42 @@
+<?php
+/**
+ * Fired when the plugin is uninstalled.
+ *
+ * Cleans up all plugin data: peptide posts, post meta, options, transients, and rewrite rules.
+ *
+ * @package PeptideSearchAI
+ */
+
+// Abort if not called by WordPress.
+if ( ! defined( 'WP_UNINSTALL_PLUGIN' ) ) {
+	exit;
+}
+
+global $wpdb;
+
+// 1. Delete all peptide custom posts and their meta.
+$peptide_ids = $wpdb->get_col(
+	"SELECT ID FROM {$wpdb->posts} WHERE post_type = 'peptide'"
+);
+
+if ( ! empty( $peptide_ids ) ) {
+	foreach ( $peptide_ids as $post_id ) {
+		wp_delete_post( (int) $post_id, true ); // Force delete, bypass trash.
+	}
+}
+
+// 2. Delete plugin options.
+delete_option( 'psa_settings' );
+
+// 3. Delete all plugin transients (validation cache, rate limits).
+$wpdb->query(
+	"DELETE FROM {$wpdb->options}
+	 WHERE option_name LIKE '_transient_psa_%'
+	    OR option_name LIKE '_transient_timeout_psa_%'"
+);
+
+// 4. Drop API logs table.
+$wpdb->query( "DROP TABLE IF EXISTS {$wpdb->prefix}psa_api_logs" ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery
+
+// 5. Flush rewrite rules to clean up the peptide post type permalinks.
+flush_rewrite_rules();