docs: add mkdocs, update links, add architecture documentation

docs/content/adr/0026-error-reporting-service.md

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+# ADR-0026: Error Reporting Service
+
+## Status
+Accepted
+
+## Context
+The platform needs error reporting for:
+- Production error tracking
+- Stack trace collection
+- Error aggregation and analysis
+- Integration with monitoring
+
+Options considered:
+1. **Sentry** - Popular, feature-rich
+2. **Rollbar** - Alternative error tracking
+3. **Custom solution** - Build our own
+4. **Logs only** - No external service
+
+## Decision
+Use **Sentry** for error reporting (optional, configurable):
+
+1. **Integration**: Via error bus sink
+2. **Configuration**: Sentry DSN from config
+3. **Context**: Include user ID, trace ID, module name
+4. **Optional**: Can be disabled for development
+
+**Rationale:**
+- Industry standard error tracking
+- Excellent Go SDK
+- Rich features (release tracking, grouping, etc.)
+- Good free tier
+- Easy to integrate
+
+## Consequences
+
+### Positive
+- Excellent error tracking
+- Rich context and grouping
+- Easy integration
+- Good free tier
+
+### Negative
+- External dependency
+- Additional cost at scale
+- Privacy considerations (data sent to Sentry)
+
+### Implementation Notes
+- Install: `github.com/getsentry/sentry-go`
+- Create Sentry sink for error bus
+- Configure via environment variable
+- Include context: user ID, trace ID, module name
+- Set up release tracking
+- Configure sampling for high-volume deployments
+