v0.5.2

Trace tree diagnostic endpoint

Adds GET /api/v1/trace-tree?trace_id=<hex> to the live server. Returns the full parent-child span hierarchy for a trace, showing service name, span name, has_rf_attrs, and nested children.

Use it to inspect the actual span topology and verify cross-service nesting:

curl http://localhost:8077/api/v1/trace-tree?trace_id=214bcda69f80bde0a4f15377165f434c | python3 -m json.tool

Also includes the v0.5.1 fix for cross-service spans not visible in the Explorer tree (same-service pass-through recursion in buildKeywords).