feat(ATL-57): Add /api/health endpoint for status monitoring

src/app/api/health/route.ts

@@ -0,0 +1,77 @@
+import { NextResponse } from "next/server";
+import { db } from "@/server/db";
+
+interface HealthCheck {
+  status: "healthy" | "unhealthy";
+  timestamp: string;
+  checks: {
+    database: {
+      status: "up" | "down";
+      latencyMs?: number;
+      error?: string;
+    };
+    lightning: {
+      status: "up" | "down" | "unknown";
+      error?: string;
+    };
+  };
+}
+
+export async function GET(): Promise<NextResponse<HealthCheck>> {
+  const startTime = Date.now();
+  const checks: HealthCheck["checks"] = {
+    database: { status: "down" },
+    lightning: { status: "unknown" },
+  };
+
+  // Check database connectivity
+  try {
+    const dbStart = Date.now();
+    await db.$queryRaw`SELECT 1`;
+    checks.database = {
+      status: "up",
+      latencyMs: Date.now() - dbStart,
+    };
+  } catch (error) {
+    checks.database = {
+      status: "down",
+      error: error instanceof Error ? error.message : "Unknown database error",
+    };
+  }
+
+  // Check Lightning/MDK connectivity
+  // For now, we just verify the env vars are set
+  // A more thorough check would create a test invoice
+  try {
+    const mdkToken = process.env.MDK_ACCESS_TOKEN;
+    const mdkMnemonic = process.env.MDK_MNEMONIC;
+
+    if (mdkToken && mdkMnemonic) {
+      checks.lightning = { status: "up" };
+    } else {
+      checks.lightning = {
+        status: "down",
+        error: "MDK credentials not configured",
+      };
+    }
+  } catch (error) {
+    checks.lightning = {
+      status: "down",
+      error: error instanceof Error ? error.message : "Unknown lightning error",
+    };
+  }
+
+  const allHealthy = 
+    checks.database.status === "up" && 
+    checks.lightning.status === "up";
+
+  const response: HealthCheck = {
+    status: allHealthy ? "healthy" : "unhealthy",
+    timestamp: new Date().toISOString(),
+    checks,
+  };
+
+  return NextResponse.json(response, {
+    status: allHealthy ? 200 : 503,
+  });
+}