[Observability] Continuous profiling: gateway endpoint and flame-graph panel

### Feature Summary
The dashboard has no way to view continuous CPU/memory profiles for a workflow, so diagnosing hot paths and resource regressions requires external tooling. This adds scoped profile retrieval and a flame-graph view in the observability dashboard.
### Proposed Solution or Design
- Backend: a gRPC-Web client to the Parca server (`ParcaClient`) with a profiles query builder and `parseProfiles`; a `ProfilesResource` exposing scoped profile queries (optional workflow and execution id), registered in `TexeraWebApplication`.
- Frontend: a profiles panel with a flame-chart component, scoped by workflow and execution id, with explicit empty states for "no samples yet" and for environments where profiling is disabled.
### Affected Area
Workflow UI, Other
### Related
Part of #4070. Depends on #5373.