Fix contradictions and stale content found during 'Start using OTel' guide authoring

Surfaced while drafting #7320. All five items are factually incorrect or contradictory in current upstream main.

1. **`elastic-agent` reference/edot-collector/upstream-collector.md** still says "Because the Managed OTLP Endpoint is not yet available for ECH…" — stale; mOTLP has been GA on ECH since 9.0. Contradicted by the mOTLP reference page frontmatter (`ech: ga`), `opentelemetry://reference/architecture/index.md`, `architecture/hosts_vms.md`, `compatibility/sdks.md`, and the `quickstart-elastic-cloud-otel-endpoint.md` prerequisite note. Related: #7653.

2. **Central configuration status mismatch** — `opentelemetry://reference/compatibility/features.md` lists "Central management of OTel SDKs" as `[Supported]`, but `central-configuration.md` is tagged `stack: preview 9.1+, serverless: unavailable`, and the `edot-sdks/index.md` feature matrix marks it Technical Preview for every SDK. Cannot be both.

3. **RUM / EDOT Browser contradiction** — `opentelemetry://reference/compatibility/limitations.md` says "Real user monitoring (RUM): RUM ingestion and visualizations are not yet available for OTel-native data", but EDOT Browser 0.3.0 is a shipped Technical Preview explicitly for RUM use cases. The limitation should be scoped to GA/production parity, not framed as unavailable.

4. **ECH quickstart architecture mismatch** — `quickstart/ech/{hosts_vms,docker,k8s}.md` instruct an edge collector to write directly to Elasticsearch using the `elasticsearch` exporter via `ELASTICSEARCH_ENDPOINT`. This contradicts `opentelemetry://reference/architecture/hosts_vms.md` (ECH → Managed OTLP Endpoint) and `elastic-agent://reference/edot-collector/modes.md` ("the only case where the `elasticsearch` exporter is recommended" = self-managed gateway). The ECH quickstarts should use the Managed OTLP Endpoint path, or at minimum note it as the recommended default for 9.0+.

5. **Rebrand miss in `apm/opentelemetry/index.md`** — The 9.5 rebrand (PR #7434) updated the `{{edot}}` substitution value but this page contains literal (non-substitution) strings that weren't reached: the H2 "Why use the Elastic Distributions of OpenTelemetry?" and six link labels "Elastic Distribution of OpenTelemetry Java/.NET/Node.js/Python/PHP/Browser". These should use the substitution or current product names.

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TriageBot — Complete

### 2026-08-10

**Type:** documentation

**Section check:**
- [✅] Problem statement: clear enough from the five listed contradictions/stale items.
- [✅] Expected outcome: implied by each item's corrective wording.
- [✅] Scope/examples: each bullet includes the affected pages and the mismatch.

**Ambiguity / scope notes:**
- None blocking.

**Cross-references:**
- All issue links are internal or already visible; no broken refs found in the body.

**Next step:** none — issue is complete.

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