Migrate metric-alert mutations (create/edit/delete) to detectors API #1277

Follow-up to #1275, which migrated the metric-alert read path (list / view / rule resolution) to the org-scoped /organizations/{org}/detectors/ endpoint. Metric-alert mutations still hit the legacy /organizations/{org}/alert-rules/ endpoint being retired 2026-08-17:

• createMetricAlertRule → POST /organizations/{org}/alert-rules/
• putMetricAlertRule (edit) + getMetricAlertRuleDocument (edit baseline fetch) → /organizations/{org}/alert-rules/{id}/
• deleteMetricAlertRule → DELETE /organizations/{org}/alert-rules/{id}/

(all in src/lib/api/alerts.ts; commands in src/commands/alert/metrics/{create,edit,delete}.ts.)

Why this is deferred from #1275

The CLI create/edit commands build a flat legacy alert-rule body (name, query, aggregate, dataset, timeWindow, triggers, projects, environment, owner). The detectors write API takes a different nested shape (dataSources / dataConditions / config). Migrating mutations means:

1. Translating the flat CLI input into the nested detector create/update payload (and back for the edit merge baseline).
2. Repointing delete to DELETE /organizations/{org}/detectors/{id}/.
3. New/updated tests for each mutation path.

Per #1274 this is also gated on the monitors/workflows write-API feature gaps tracked in #1142. This mirrors the issue-alert precedent (#1215/#1216), which migrated reads first and deferred mutations.

Scope

• createMetricAlertRule → detectors POST
• putMetricAlertRule + edit baseline fetch → detectors PUT/GET
• deleteMetricAlertRule → detectors DELETE
• Update create/edit/delete command body builders + tests

Refs #1274, #1275, getsentry/toolkit#1482, #1142