feat: add OpenTelemetry logging for PostHog and fix client-side errors

[bokelley]

Summary

• Add OpenTelemetry logging integration for PostHog Logs feature
• Fix client-side JavaScript errors shown in PostHog Error Tracking

Changes

OpenTelemetry Logging

• New server/src/utils/otel-logs.ts module with OTLP HTTP exporter
• Integrates with Pino logger via setLogHook()
• Configurable min log level via OTEL_MIN_LOG_LEVEL env var (default: 30 = info)
• Configurable service name via OTEL_SERVICE_NAME env var
• Reads version from package.json for accurate version tracking
• Batch processing for performance (512 logs per batch, 5s flush interval)

Client-Side Error Fixes

• admin-prospects.html: Fix quickInvoice() referencing non-existent .invoice-step elements
• dashboard.html: Add optional chaining for DashboardNav.showLeadershipNav to handle cached JS files

Performance Optimization

• Add early return in logger hook when no hooks are set to avoid unnecessary argument parsing

Test plan

• TypeScript compiles without errors
• All unit tests pass
• Tested invoice modal in admin prospects page (no JS errors)
• Tested dashboard page (no JS errors)
• Verified OpenTelemetry initialization in Docker logs

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