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/src/services/billing/billing-service.ts

@@ -1,7 +1,7 @@
 import type Redis from 'ioredis'
 
 import type { Database } from '../../libs/db'
-import type { RevenueMetrics } from '../../libs/otel'
+import type { RevenueMetrics } from '../../otel'
 import type { ConfigKVService } from '../config-kv'
 
 import { useLogger } from '@guiiai/logg'

apps/server/src/services/billing/flux-meter.ts

@@ -1,6 +1,6 @@
 import type Redis from 'ioredis'
 
-import type { RevenueMetrics } from '../../libs/otel'
+import type { RevenueMetrics } from '../../otel'
 import type { BillingService } from './billing-service'
 
 import { useLogger } from '@guiiai/logg'

apps/server/src/services/characters.ts

@@ -1,5 +1,5 @@
 import type { Database } from '../libs/db'
-import type { EngagementMetrics } from '../libs/otel'
+import type { EngagementMetrics } from '../otel'
 
 import { useLogger } from '@guiiai/logg'
 import { and, eq, isNull, or, sql } from 'drizzle-orm'

apps/server/src/services/chats.ts

@@ -1,7 +1,7 @@
 import type { MessageRole, WireMessage } from '@proj-airi/server-sdk-shared'
 
 import type { Database } from '../libs/db'
-import type { EngagementMetrics } from '../libs/otel'
+import type { EngagementMetrics } from '../otel'
 
 import { useLogger } from '@guiiai/logg'
 import { and, eq, gt, inArray, isNull, sql } from 'drizzle-orm'

apps/server/src/services/email.ts

@@ -1,6 +1,6 @@
 import type { Logger } from '@guiiai/logg'
 
-import type { EmailMetrics } from '../libs/otel'
+import type { EmailMetrics } from '../otel'
 
 import { useLogger } from '@guiiai/logg'
 import { errorMessageFrom } from '@moeru/std'