Add verbose request logs page

[BenItBuhner]

Superseded

This branch was superseded by the clean OSP-102 branch/PR because it accidentally included unrelated branch history while preserving the dirty worktree. Please review the clean replacement PR instead.

Original summary

• Add a /logs admin page that lists recent requests and shows selected request details.
• Reuse the existing event timeline to surface routing, fallback, key, proxy, and enforcement events.
• Enrich request trace events with API key source hints and masked proxy rotation metadata.
• Add backend coverage for key/proxy metadata in admin event traces.

Testing

• Superseded; see the clean replacement PR for current validation.