Fix guardian mode: create missing tables on startup, fix conversations column name

- Add CREATE TABLE IF NOT EXISTS for guardian_config and guardian_events in
  reactor lifespan so tables are created automatically on next restart
- Fix conversations column bug: reactor used 'message' but schema has 'content';
  fix INSERT and SELECT queries to use content (SELECT aliases it as 'message'
  so the JSON response key stays the same)
- Add guardian tables to schema.sql for documentation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X8tDRrQqgLjqXebMCBNcP3

db/schema.sql

@@ -441,4 +441,41 @@ CREATE TABLE `users` (
 /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
 /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
 
+--
+-- Table structure for table `guardian_config`
+--
+
+CREATE TABLE IF NOT EXISTS `guardian_config` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `key_name` varchar(64) NOT NULL,
+  `value` varchar(255) NOT NULL DEFAULT '',
+  `updated_at` datetime DEFAULT current_timestamp() ON UPDATE current_timestamp(),
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `uk_key` (`key_name`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
+--
+-- Table structure for table `guardian_events`
+--
+
+CREATE TABLE IF NOT EXISTS `guardian_events` (
+  `id` int(11) NOT NULL AUTO_INCREMENT,
+  `event_type` varchar(64) NOT NULL,
+  `severity` enum('info','warning','critical') NOT NULL DEFAULT 'info',
+  `agent_id` varchar(64) NOT NULL DEFAULT '',
+  `hostname` varchar(128) NOT NULL DEFAULT '',
+  `metric` varchar(64) NOT NULL DEFAULT '',
+  `value` float NOT NULL DEFAULT 0,
+  `threshold` float NOT NULL DEFAULT 0,
+  `message` text NOT NULL,
+  `ai_analysis` text NOT NULL DEFAULT '',
+  `acknowledged` tinyint(1) NOT NULL DEFAULT 0,
+  `created_at` datetime NOT NULL DEFAULT current_timestamp(),
+  PRIMARY KEY (`id`),
+  KEY `idx_severity` (`severity`),
+  KEY `idx_ack` (`acknowledged`),
+  KEY `idx_created` (`created_at`),
+  KEY `idx_agent` (`agent_id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+
 -- Dump completed on 2026-06-29 23:15:44