feat: add PROMPT subject support for NGT (Agentforce Studio) test creation @W-23524165@

[niharpatel-salesforce]

What does this PR do?

Demo video link

Adds client-side support for the PROMPT subject type (prompt template testing) to the NGT (Agentforce Studio) sf agent test create code path, alongside the existing AGENT subject type. Covers the full round trip:

• Types (src/types.ts, src/index.ts): new AiPromptTestCase, AiTestCasePromptInputXml, NgtPromptInputSet, NgtPromptTestCase, discriminated by subjectType: 'AGENT' | 'PROMPT'.
• YAML → metadata XML (convertToTestingMetadata + new toPromptInputsXml): serializes a PROMPT spec's promptInput slots into AiTestingDefinition XML.
• Metadata XML → spec (convertToNgtSpec + new parsePromptTestCaseXml; collapseContiguousTestCases genericized): parses a deployed PROMPT AiTestingDefinition back into an NgtTestSpec, including multi-invocation fan-out/collapse.
• Validation (validateNgtSpec + new validatePromptTestCases, shared validateScorers extracted): PROMPT specs get structural + promptInput content checks (non-blank referenceName/value), and correctly skip the AGENT-only multi-agent-handoff / task_resolution+conversationHistory / conversationHistory-index rules.
• Scorer validation (src/ngtScorerCatalog.ts, validateScorers): each catalog scorer now declares which subject types it supports. AGENT keeps all 11 existing scorers; PROMPT supports 5 (coherence, conciseness, factuality, completeness, response_match). Using any other catalog scorer on a PROMPT spec now emits a Lifecycle warning instead of passing through silently — the deploy still proceeds and is validated server-side. AGENT behavior is unchanged.
• Wiring (AgentTest.create()): skips the BotDefinition.IsMultiAgent org lookup for PROMPT subjects, since multi-agent handoff is structurally an AGENT-only concept.
• Reorganized the subject-type dispatch in convertToTestingMetadata, convertToNgtSpec, and validateNgtSpec into small per-subject handler functions routed through one shared helper. The default path is the existing AGENT path; the PROMPT path is only taken when subjectType is exactly PROMPT. No behavior change for the AGENT path.
• 3 new user-facing message keys in messages/agentTest.md, 2 new fixtures (test/fixtures/ngt-prompt-*), and unit tests for every new code path.

Example PROMPT spec:

name: SummarizeCasePromptSuite
description: Validates the SummarizeCase prompt template.
subjectType: PROMPT
subjectName: SummarizeCasePrompt
subjectVersion: v3
testCases:
  - inputs:
      - promptInput:
          - referenceName: CaseDescription
            value: Customer reports login failures since yesterday.
          - referenceName: CustomerTone
            value: frustrated
    scorers:
      - name: factuality
      - name: completeness
      - name: response_match
        expected: A concise, accurate case summary

sf agent test create --spec ./summarize-case-spec.yaml --test-runner agentforce-studio --api-name SummarizeCasePromptSuite --target-org myOrgAlias

Testing:

• Unit: yarn test — 435 passing, 1 pending, 0 failing, coverage thresholds met.
• Manually verified end-to-end against a live org (sf agent test create --test-runner agentforce-studio, linked build of this branch into plugin-agent) across 16 scenarios spanning both subject types — validation failures, server-side rejections, and successful deploys with XML inspection:

#	Scenario	Result	As expected?
1	AGENT subject: full 11-scorer catalog on a single test case	Client-side ngtTaskResolutionRequiresConversationHistory (fixture's task_resolution scorer needs conversationHistory)	Yes
2	AGENT subject: baseline smoke test	Deploy failed: BotVersion not found (org-state — bot has no deployed version)	Yes
3	AGENT subject: baseline smoke test (second bot)	Deploy failed: BotVersion not found (org-state)	Yes
4	PROMPT subject: baseline multi-invocation spec	Deployed successfully	Yes
5	PROMPT subject: baseline multi-invocation spec (variant)	Deployed successfully	Yes
6	PROMPT subject: AGENT-only scorer (topic_sequence_match)	Client warning ("not supported for subject type 'PROMPT'"); deploy also rejected server-side	Yes
7	PROMPT subject: blank referenceName	Client-side ngtPromptInputMissingReferenceName	Yes
8	PROMPT subject: blank value	Client-side ngtPromptInputMissingValue	Yes
9	PROMPT subject: empty promptInput: list	Client-side ngtPromptInputSetEmpty	Yes
10	Misspelled subjectType: PROMT	Deploy failed: BotVersion not found (took the AGENT path)	Yes — the default path is AGENT; the PROMPT path is only taken when subjectType is exactly PROMPT
11	PROMPT subject: scorer missing expected:	Client-side ngtScorerMissingExpected	Yes
12	PROMPT subject: multi-invocation fan-out	Deployed successfully	Yes
13	PROMPT subject: non-adjacent matching scorer sets	Deployed successfully (no false collapse)	Yes
14	PROMPT subject: unquoted numeric value	Deployed successfully	Yes
15	PROMPT subject: quality scorer (coherence) with expected: supplied anyway	XML omits <expectedValue>; deployed successfully	Yes
16	PROMPT subject: scorer unknown to the local catalog	Client warning only; deploy rejected server-side with the org's full scorer allow-list	Yes

What issues does this PR fix or reference?

@W-23524165@