observability: finalize Phase 1 primitive instrumentation & tests

[theinterneti]

Background:
Several branches and PR #26 cover different observability aspects. We want a minimal, verifiable Phase 1.

Phase 1 Goals:

• Ensure all core primitives create OpenTelemetry spans with consistent naming.
• Add unit tests in platform/primitives/tests/ that:
  • Verify span creation and attributes.
  • Assert no regressions in error handling.
• Confirm integration with tta-observability-integration for:
  • Basic metrics (latency, success/failure counts).
• Update:
  • docs/observability/* to match actual behavior.
  • PRIMITIVES_CATALOG.md entries for observability primitives.

Cleanup:

• Close PR feat: Phase 1 Workflow Enhancements - Observability, API Testing & Validation #26 after extracting useful changes.

Links:

• PR feat: Phase 1 Workflow Enhancements - Observability, API Testing & Validation #26
• docs/OBSERVABILITY_SETUP_COMPLETE.md