feat(API-11): Route API calls through AgilitonAPI gateway

Add gateway-first pattern: when AGILITON_API_KEY is set, route all
external API calls through the gateway with X-API-Key auth. Falls back
to direct API access when gateway is unavailable.

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

node_modules/side-channel-list/.nycrc

@@ -0,0 +1,13 @@
+{
+	"all": true,
+	"check-coverage": false,
+	"reporter": ["text-summary", "text", "html", "json"],
+	"lines": 86,
+	"statements": 85.93,
+	"functions": 82.43,
+	"branches": 76.06,
+	"exclude": [
+		"coverage",
+		"test"
+	]
+}