feat(server/otel): restructure observability metrics and add active sessions gauge

- Moved RateLimitMetrics import path to a more centralized location.
- Introduced a new file for active sessions gauge to track user sessions in the database.
- Updated index.ts to include new metrics and ensure proper initialization of observability metrics.
- Modified various routes and services to utilize the new observability structure.
- Added smoke tests for HTTP and WebSocket metrics to ensure proper metric registration and functionality.
- Enhanced error handling for metrics reading failures to improve observability.

apps/server/package.json

@@ -6,13 +6,14 @@
   "scripts": {
     "apply:env": "dotenvx run -f .env.local --overload --ignore=MISSING_ENV_FILE",
     "auth:generate": "pnpm run apply:env -- better-auth generate --config src/scripts/auth.ts --output src/schemas/accounts.ts -y",
-    "dev": "pnpm run apply:env -- tsx --import ./instrumentation.mjs --watch src/bin/run.ts api",
-    "start": "pnpm run apply:env -- tsx --import ./instrumentation.mjs src/bin/run.ts api",
-    "server": "pnpm run apply:env -- tsx --import ./instrumentation.mjs src/bin/run.ts",
+    "dev": "pnpm run apply:env -- tsx --import ./instrumentation.ts --watch src/bin/run.ts api",
+    "start": "pnpm run apply:env -- tsx --import ./instrumentation.ts src/bin/run.ts api",
+    "server": "pnpm run apply:env -- tsx --import ./instrumentation.ts src/bin/run.ts",
     "build": "tsc -b",
     "typecheck": "tsc --noEmit",
     "db:generate": "drizzle-kit generate",
-    "db:push": "pnpm run apply:env -- drizzle-kit push"
+    "db:push": "pnpm run apply:env -- drizzle-kit push",
+    "otel:dashboards": "tsx otel/grafana/dashboards/build.ts"
   },
   "dependencies": {
     "@better-auth/drizzle-adapter": "^1.6.5",