feat(observability): traces end-to-end (gateway + UI panel)

[Ma77Ball]

What changes were proposed in this PR?

Distributed-trace retrieval through the gateway plus a trace-tree UI panel.
Backend:

• Trace query builder and parseTraces.
• TracesResource exposing trace retrieval by id, with id validation and scope enforcement at the gateway.
  Frontend:
• Traces panel rendering spans as a tree built from parent-span relationships, with pivot-from-log so a log row can open its trace directly. Span fields are bound with text interpolation only.

Any related issues, documentation, or discussions?

Closes: #5373
Part of #4070. Stacked on #5380.

How was this PR tested?

• Backend specs for the trace query builder and parser; sbt scalafmtCheckAll passes.
• Frontend traces-panel specs, including the span-tree builder; prettier-eslint and eslint pass.
• Compile and the full test suites run in this PR's CI.

Was this PR authored or co-authored using generative AI tooling?

Co-authored with Claude Opus 4.8 in compliance with ASF

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.06767% with 122 lines in your changes missing coverage. Please review.
✅ Project coverage is 51.98%. Comparing base (ce91924) to head (f306ba9).

Files with missing lines	Patch %	Lines
...observability/logs-panel/logs-panel.component.html	56.92%	55 Missing and 1 partial ⚠️
...rvability/traces-panel/traces-panel.component.html	44.11%	19 Missing ⚠️
...r/observability/logs-panel/logs-panel.component.ts	84.46%	3 Missing and 13 partials ⚠️
...servability/traces-panel/traces-panel.component.ts	74.19%	13 Missing and 3 partials ⚠️
...rvability/metrics-panel/metrics-panel.component.ts	84.21%	5 Missing and 4 partials ⚠️
...ervice/user/observability/observability.service.ts	91.66%	2 Missing and 1 partial ⚠️
...nent/user/observability/observability.component.ts	92.59%	2 Missing ⚠️
...nt/user/observability/observability.component.html	95.83%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5381      +/-   ##
============================================
+ Coverage     51.87%   51.98%   +0.10%     
+ Complexity     2467     2424      -43     
============================================
  Files          1067     1069       +2     
  Lines         41258    41601     +343     
  Branches       4437     4487      +50     
============================================
+ Hits          21402    21625     +223     
- Misses        18595    18715     +120     
  Partials       1261     1261              

Flag	Coverage Δ		*Carryforward flag
access-control-service	42.22% <ø> (ø)
agent-service	33.76% <ø> (ø)		Carriedforward from eac23d2
amber	52.27% <ø> (-0.58%)	⬇️	Carriedforward from eac23d2
computing-unit-managing-service	1.65% <ø> (ø)
config-service	56.06% <ø> (ø)
file-service	38.32% <ø> (ø)
frontend	47.34% <77.06%> (+0.96%)	⬆️
pyamber	90.67% <ø> (-0.02%)	⬇️	Carriedforward from eac23d2
python	90.83% <ø> (ø)		Carriedforward from eac23d2
workflow-compiling-service	58.69% <ø> (ø)

*This pull request uses carry forward flags. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.