feat(08-01): add Prometheus /metrics endpoint with prom-client

- Install prom-client library for Prometheus metrics
- Create src/lib/server/metrics.ts with default Node.js process metrics
- Add /metrics endpoint that returns Prometheus-format text
- Exposes CPU, memory, heap, event loop metrics

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package-lock.json

@@ -12,6 +12,7 @@
 				"better-sqlite3": "^12.6.2",
 				"drizzle-orm": "^0.45.1",
 				"nanoid": "^5.1.6",
+				"prom-client": "^15.1.3",
 				"sharp": "^0.34.5",
 				"svelecte": "^5.3.0",
 				"svelte-gestures": "^5.2.2",
@@ -1626,6 +1627,15 @@
 				"@jridgewell/sourcemap-codec": "^1.4.14"
 			}
 		},
+		"node_modules/@opentelemetry/api": {
+			"version": "1.9.0",
+			"resolved": "https://registry.npmjs.org/@opentelemetry/api/-/api-1.9.0.tgz",
+			"integrity": "sha512-3giAOQvZiH5F9bMlMiv8+GSPMeqg0dbaeo58/0SlA9sxSqZhnUtxzX9/2FzyhS9sWQf5S0GJE0AKBrFqjpeYcg==",
+			"license": "Apache-2.0",
+			"engines": {
+				"node": ">=8.0.0"
+			}
+		},
 		"node_modules/@playwright/test": {
 			"version": "1.58.1",
 			"resolved": "https://registry.npmjs.org/@playwright/test/-/test-1.58.1.tgz",
@@ -2638,6 +2648,12 @@
 				"file-uri-to-path": "1.0.0"
 			}
 		},
+		"node_modules/bintrees": {
+			"version": "1.0.2",
+			"resolved": "https://registry.npmjs.org/bintrees/-/bintrees-1.0.2.tgz",
+			"integrity": "sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw==",
+			"license": "MIT"
+		},
 		"node_modules/bl": {
 			"version": "4.1.0",
 			"resolved": "https://registry.npmjs.org/bl/-/bl-4.1.0.tgz",
@@ -5059,6 +5075,19 @@
 				"url": "https://github.com/prettier/prettier?sponsor=1"
 			}
 		},
+		"node_modules/prom-client": {
+			"version": "15.1.3",
+			"resolved": "https://registry.npmjs.org/prom-client/-/prom-client-15.1.3.tgz",
+			"integrity": "sha512-6ZiOBfCywsD4k1BN9IX0uZhF+tJkV8q8llP64G5Hajs4JOeVLPCwpPVcpXy3BwYiUGgyJzsJJQeOIv7+hDSq8g==",
+			"license": "Apache-2.0",
+			"dependencies": {
+				"@opentelemetry/api": "^1.4.0",
+				"tdigest": "^0.1.1"
+			},
+			"engines": {
+				"node": "^16 || ^18 || >=20"
+			}
+		},
 		"node_modules/pump": {
 			"version": "3.0.3",
 			"resolved": "https://registry.npmjs.org/pump/-/pump-3.0.3.tgz",
@@ -5623,6 +5652,15 @@
 				"node": ">=6"
 			}
 		},
+		"node_modules/tdigest": {
+			"version": "0.1.2",
+			"resolved": "https://registry.npmjs.org/tdigest/-/tdigest-0.1.2.tgz",
+			"integrity": "sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA==",
+			"license": "MIT",
+			"dependencies": {
+				"bintrees": "1.0.2"
+			}
+		},
 		"node_modules/tinyglobby": {
 			"version": "0.2.15",
 			"resolved": "https://registry.npmjs.org/tinyglobby/-/tinyglobby-0.2.15.tgz",

package.json

@@ -39,6 +39,7 @@
 		"better-sqlite3": "^12.6.2",
 		"drizzle-orm": "^0.45.1",
 		"nanoid": "^5.1.6",
+		"prom-client": "^15.1.3",
 		"sharp": "^0.34.5",
 		"svelecte": "^5.3.0",
 		"svelte-gestures": "^5.2.2",

src/lib/server/metrics.ts

@@ -0,0 +1,7 @@
+import { Registry, collectDefaultMetrics } from 'prom-client';
+
+// Create a custom registry for metrics
+export const registry = new Registry();
+
+// Collect default Node.js process metrics (CPU, memory, event loop, etc.)
+collectDefaultMetrics({ register: registry });

src/routes/metrics/+server.ts

@@ -0,0 +1,22 @@
+import type { RequestHandler } from './$types';
+import { registry } from '$lib/server/metrics';
+
+export const GET: RequestHandler = async () => {
+	try {
+		const metrics = await registry.metrics();
+
+		return new Response(metrics, {
+			status: 200,
+			headers: {
+				'Content-Type': registry.contentType
+			}
+		});
+	} catch (error) {
+		console.error('Metrics collection failed:', error);
+
+		return new Response('Metrics unavailable', {
+			status: 500,
+			headers: { 'Content-Type': 'text/plain' }
+		});
+	}
+};