[autonomy-atomicity] Stale workflow name in trigger-ci-workflows.sh causes monitor dispatch failures

## Autonomy / Atomicity Findings

### 1. `MONITORS` registry contains a stale workflow name
**Category:** Manual routing/registration
**File(s):** `scripts/trigger-ci-workflows.sh` (lines 39-44, 122-129), `.github/workflows/trigger-internal-downstream-health.yml` (line 3)

**Problem:**
The central monitor registry in `scripts/trigger-ci-workflows.sh` includes:

- `Trigger Estc Downstream Health` (line 41)

But the actual workflow name is:

- `Trigger Internal Downstream Health` (`.github/workflows/trigger-internal-downstream-health.yml`, line 3)

Dispatch uses the registry string directly:

- `gh workflow run "$name" ...` (`scripts/trigger-ci-workflows.sh`, line 125)

So this monitor entry fails at runtime (`dispatch failed`) instead of running.

This is also a parallel-change hotspot: every workflow rename/addition requires editing this shared array, which increases merge conflicts and drift risk.

**Suggested fix:**
- Replace hardcoded workflow-name arrays with generated discovery from `trigger-*.yml` workflow names (or one canonical registry file consumed by both compile and dispatch scripts).
- Add a CI validation check that each scripted workflow name resolves to an existing trigger workflow.

## Suggested Actions
- [ ] Update `scripts/trigger-ci-workflows.sh` to stop relying on hardcoded monitor names.
- [ ] Add validation to fail CI when script registries reference non-existent workflow names.
- [ ] Correct the current stale entry (`Estc` -> `Internal`) as an immediate fix.

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[What is this?](https://ela.st/github-ai-tools) | [From workflow: Trigger Autonomy Atomicity Analyzer](https://github.com/elastic/ai-github-actions/actions/runs/23755612583)

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