docs: add builder observability page

[decofe]

Summary

Adds a new dev-docs page documenting Tempo builder observability tooling, data sources, and investigation workflow.

Content

• Workflow: outlier investigation loop (ValScope → BlockScope drill-down)
• ValScope: what it shows, key pages, validator configs, testnet/mainnet URLs
• BlockScope: execution-level dashboard, trace breakdowns, mempool overlap
• Data sources table: all 5 services (VLogs external/internal, VM external/internal, Tempo Traces) with env vars, descriptions, and testnet/mainnet Tailscale endpoints
• Known outlier patterns: execution cache mutex, late build start, persistence during building, long newPayload
• Limitations: no external validator traces, instrumentation requires release, log parsing gaps

Context

Consolidates context from two Slack threads about tempo perf observability (alexey + joshie + chia).

Testing

bun run check and bun run build pass.

Prompted by: yk

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Project	Deployment	Actions	Updated (UTC)
tempo-docs	Building	Preview, Comment	Mar 11, 2026 4:09am