feat: AI usage logging (AiLogger, ai_logs table, admin view)

- AiLogger.php: new service, inserts into ai_logs on every AI call
- ai_logs table: added to migrate.php (provider, model, call_type, tokens, duration_ms)
- AiBot: logs chat, media_response, nlu calls with timing and token counts
- MediaTranscriber: logs whisper, geminiAudio, openaiVision, geminiVision, claudeVision
- /admin/ai-logs: paginated table with provider/company filter
- Layout.php: added IA Logs nav link
- index.php: require AiLogger before AiBot; added GET /admin/ai-logs route

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

setup/migrate.php

@@ -257,6 +257,27 @@ $db->exec("
     ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
 ");
 
+// ─── AI usage logs ───────────────────────────────────────────────────────────
+$db->exec("
+    CREATE TABLE IF NOT EXISTS ai_logs (
+        id            BIGINT       NOT NULL AUTO_INCREMENT PRIMARY KEY,
+        company_id    INT          DEFAULT NULL,
+        phone_number  VARCHAR(20)  DEFAULT NULL,
+        provider      VARCHAR(20)  NOT NULL,
+        model         VARCHAR(60)  NOT NULL DEFAULT '',
+        call_type     VARCHAR(30)  NOT NULL DEFAULT 'chat',
+        input_preview VARCHAR(500) DEFAULT NULL,
+        output_preview VARCHAR(500) DEFAULT NULL,
+        tokens_in     INT          DEFAULT NULL,
+        tokens_out    INT          DEFAULT NULL,
+        duration_ms   INT          DEFAULT NULL,
+        created_at    DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP,
+        INDEX idx_company  (company_id),
+        INDEX idx_provider (provider),
+        INDEX idx_created  (created_at)
+    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+");
+
 // ─── Campo erp_active_users en companies ──────────────────────────────────────
 try {
     $db->exec("ALTER TABLE companies ADD COLUMN erp_active_users INT DEFAULT 0 AFTER is_active");