feat: enable Cloudflare Workers observability (logs + traces)

Add observability config to wrangler.jsonc with logs and traces enabled,
100% sampling, and persistence. Free tier feature — no code changes needed.

wrangler.jsonc

@@ -23,6 +23,21 @@
 				"max_retries": 3
 			}
 		]
+	},
+	"observability": {
+		"enabled": false,
+		"head_sampling_rate": 1,
+		"logs": {
+			"enabled": true,
+			"head_sampling_rate": 1,
+			"persist": true,
+			"invocation_logs": true
+		},
+		"traces": {
+			"enabled": true,
+			"persist": true,
+			"head_sampling_rate": 1
+		}
 	}
 	// Secrets (set via `wrangler secret put`):
 	// BOT_TOKEN - Telegram bot token