Implement frontend and backend observability alignment

Align frontend and backend error observability with correlation IDs and
structured telemetry for distributed tracing across systems.

Backend changes:
- Add CorrelationIdMiddleware to generate/extract correlation IDs
- Include correlation_id in all ErrorResponse objects
- Store correlation ID in structlog contextvars for automatic inclusion in logs
- Add correlation ID to response headers (X-Correlation-ID)

Frontend changes:
- API client automatically generates session-scoped UUID4 and includes
  X-Correlation-ID header in all requests
- Extract correlation ID from API error responses
- Update error handlers to use telemetry with correlation IDs
- Add telemetry logging to ErrorBoundary, PageErrorBoundary, SectionErrorBoundary
- Implement redaction utilities for privacy-safe logging of sensitive data

Documentation:
- Add observability guidelines to Web-Development.md
  * Correlation ID usage patterns
  * Privacy & security best practices
  * Telemetry event structure
  * Redaction utilities for sensitive data
- Add distributed tracing architecture section to Architecture.md
  * Correlation ID flow across frontend/backend
  * Example troubleshooting scenario
  * Implementation details for future enhancements

Testing:
- Add comprehensive tests for correlation middleware
- Update error boundary tests to verify telemetry integration
- Verify TypeScript and ESLint pass with no warnings

Fixes: Issue #40 - Frontend and backend observability are not aligned

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docs/Tasks.md

@@ -1,43 +1,3 @@
-## 38) History archive query paths may need explicit indexing plan
-- Where found:
-	- [backend/app/db.py](backend/app/db.py)
-	- [backend/app/repositories/history_archive_repo.py](backend/app/repositories/history_archive_repo.py)
-- Why this is needed:
-	- Large archive datasets can degrade filter/sort performance.
-- Goal:
-	- Add indexes aligned with real query patterns.
-- What to do:
-	- Benchmark common history queries.
-	- Add migration with targeted indexes.
-- Possible traps and issues:
-	- Extra indexes increase write cost and DB size.
-- Docs changes needed:
-	- Add DB performance/indexing section for history.
-- Doc references:
-	- [Docs/Backend-Development.md](Docs/Backend-Development.md)
-	- https://www.sqlite.org/queryplanner.html
-
----
-
-## 39) No explicit DI container strategy for backend service graph
-- Where found:
-	- [backend/app/dependencies.py](backend/app/dependencies.py)
-	- [backend/app/services](backend/app/services)
-- Why this is needed:
-	- Dependency construction and lifecycle are partly implicit.
-- Goal:
-	- Define a clear dependency wiring pattern for services and repositories.
-- What to do:
-	- Create service composition root pattern and document usage.
-- Possible traps and issues:
-	- Over-engineering if container abstraction is too heavy for current size.
-- Docs changes needed:
-	- Add dependency wiring chapter.
-- Doc references:
-	- [Docs/Architekture.md](Docs/Architekture.md)
-
----
-
 ## 40) Frontend and backend observability are not aligned
 - Where found:
 	- [backend/app/main.py](backend/app/main.py)