docs: Migrate comprehensive telemetry documentation to published docs

[ajbozarth]

Migrate telemetry docs from docs/dev/ to published docs

Problem

docs/dev/telemetry.md (688 lines) contains comprehensive telemetry documentation that should be published. Only content in docs/docs/ appears on the documentation site.

Missing from published docs:

• OTLP logging export configuration
• Detailed Prometheus exporter setup
• Comprehensive troubleshooting sections
• Backend support comparison tables
• Future enhancements roadmap

Published docs (docs/docs/evaluation-and-observability/) have similar but incomplete coverage (189 + 235 lines total).

Why not a simple move?

• Content overlaps with existing published docs but uses different structures
• Needs merging/deduplication, not just moving
• Published docs require specific formatting (frontmatter, no H1 in body, markdownlint compliance)

Tasks

1. Merge docs/dev/telemetry.md content with existing published docs
2. Ensure all content follows published docs conventions
3. Update cross-references
4. Remove or archive docs/dev/telemetry.md after migration

[ajbozarth]

I'll pick this up once I'm done with #608

[ajbozarth]

Now that #653 is open I'll start work on this on Monday and open a PR once #653 is merged (since it updates the doc)