docs: cover the keep-in-Maintainerr-only collection option

[enoch85]

Addresses the drift report in #159, checked against a local clone of Maintainerr at 14585915.

What was added

Doc	Edit	Upstream
docs/Rules.mdx	Keep in Maintainerr only row in the General parameter table, plus a paragraph on what it is for, that turning it on tears down an existing media-server collection and turning it off lets the next run recreate it, and that it is mutually exclusive with Custom collection	1ce589e2, refined by b5e4206a (#3579)
docs/Collections.md	Note under Media Server, which stated flatly that a collection is reflected in your media server. Says what the opt-in changes and what still runs	1ce589e2
static/openapi-spec/maintainerr_api_specs.yaml	GET /api/settings/telemetry/preview, GET /api/settings/telemetry/status, POST /api/settings/telemetry	854e9ff1, 1705d9e8

Already covered by prior PRs

• The weekly usage report and the TELEMETRY variable are documented in docs: describe the anonymous weekly usage report in Security #158. I re-verified both against 1705d9e8 and bfbcc0ca rather than assuming they still held:
  • bfbcc0ca drops only a paragraph from About. The Settings > About > Help us improve it entry point that Security.md names is still there.
  • clientId now seeds the sample-week draw, but it stays local and is never sent, so "no identifier of any kind" is still accurate. telemetry.service.spec.ts asserts the serialized payload contains neither the key nor its value.
  • 1705d9e8 drops locale and adds collectionItems to the payload. Security.md describes the report in categories rather than field by field, so it needs no change.

Deliberately skipped

Item	Why
639bf9f7 *arr exclusion tag across several instances	Restores the behaviour Add list exclusions already promises. Nothing in the docs claimed the single-instance limit
d888b1b1, b5e4206a shared-collection teardown	Internal correctness. No documented behaviour changes
7200b7ba monaco served locally	Build and asset change with no user-facing surface
TELEMETRY_URL	Collector base-URL override for local testing. Not in the upstream ARCHITECTURE env list, so not user-facing
docs/API.md	Curated "notable endpoints" page for integrators. The telemetry settings endpoints are not that, and the spec now carries them
Migrations AddKeepCollectionInMaintainerrOnly, AddTelemetryEnabled	Both are covered by the behaviour above; neither changes anything in Migration.md or Configuration.md

Notes

• The spec descriptions are hand-written, matching how docs: cover remaining next-release drift for rules, notifications, and Tracearr API #140, docs: cover the bulk media actions rework and Tracearr server binding #146 and docs: bound the deletion window and cover the background overlay run #156 maintained this file. introspectComments is off upstream, so the generator would not produce them. The request body follows the shape the plugin emits for a Zod-validated body, as on POST /api/settings/metadata-provider.
• npm run build is clean, the YAML parses, and the new Rules.mdx#general link resolves to a real anchor inside the same docs version.