feat(testing-agentforce): NGT (Agentforce Studio) authoring + result-shape support

[BunnyBlit]

Summary

Adds Mode B support for NGT (AiTestingDefinition) to /testing-agentforce while keeping the legacy (AiEvaluationDefinition) path fully working. The skill now detects which runner the org/project supports, picks the right path automatically, and surfaces docs for both shapes. Verified end-to-end against a real org.

What's in this PR

• Detection probe — reads sourceApiVersion from sfdx-project.json; selects NGT when >= 66.0, legacy below. Falls back gracefully if the org rejects NGT metadata even on a 66.0 project.
• Pre-Run Probe — queries BotVersion.Status = 'Active' before running tests. Without this, sf agent test run silently returns testCases: [] for NGT or all-RETRY for legacy. Documented + scripted in SKILL.md.
• NGT authoring reference (references/ngt-batch-testing.md, new file, ~520 lines) — 11-scorer catalog, multi-input cases, task_resolution conversation-history rules, multi-agent subjects, --from-definition round-trip caveats, four hard authoring rules with deploy-time error signatures.
• Result-shape reference (references/test-report-format.md) — new Legacy Result JSON Shape section with the XML→JSON assertion-name mapping (topic_sequence_match → topic_assertion, etc.) and the no-active-version failure shape. NGT result shape with testScorerResults[] container, JSON-encoded subjectResponse/scorerResponse, per-grade field presence.
• Troubleshooting — entries for the four NGT authoring deploy errors (DeveloperName, name/--api-name mismatch, 100-char description cap, silent empty cases), plus the legacy RETRY-mode failure analog.
• SKILL.md — Mode B forks early on the detection-probe outcome; CRITICAL callouts for the four hard authoring rules; Pre-Run Probe section before deploy-and-run.

Integration testing

Validated end-to-end against NGA_ASA_Orchestrator (NGT) and OrderHelp_Legacy (legacy) on a live OrgFarm org. Both paths:

• ran the detection probe correctly
• authored a valid YAML spec
• compiled YAML → metadata XML
• deployed via sf project deploy start
• ran the suite via sf agent test run
• returned results matching the documented JSON envelope

Test plan

• Detection probe picks NGT on a 66.0 project, legacy on a 64.0 project
• All four CRITICAL authoring rules in references/ngt-batch-testing.md produce the documented error when violated
• Pre-Run Probe halts the run when the subject bot has no Active BotVersion
• Legacy result envelope verified: testCases[].testResults[] with name ∈ {topic_assertion, actions_assertion,
  output_validation}
• NGT result envelope verified: testCases[].testScorerResults[] with JSON-encoded scorerResponse containing
  status/score/reasoning/actualValue/expectedValue