feat: implement SvelteKit frontend telemetry module

[jayfalls]

Summary

Implement SvelteKit frontend telemetry module.

Files

• frontend/src/lib/telemetry/index.ts - Main telemetry module
• frontend/src/lib/telemetry/trace.ts - Trace context
• frontend/src/lib/telemetry/error.ts - Error tracking
• frontend/src/lib/telemetry/metrics.ts - Performance metrics

Requirements

• OpenTelemetry browser SDK integration
• Trace context injection into fetch/XHR
• JavaScript error tracking (unhandled exceptions)
• Performance monitoring (page load, time-to-interactive)
• Exports trace_id for backend correlation

Acceptance Criteria

• Module compiles
• Error tracking captures exceptions
• Performance metrics captured
• Trace context propagates to backend

Design Docs

Read design/units/observability/ before starting:

• fsd.md
• architecture.md
• implementation.md

PR: (will be created)

[jayfalls]

/oc implement this