docs(real-time-metrics): rework the Real-Time Metrics section and split its chart catalog into dashboard reference pages

[marcus-souza-azion]

What & why

Branch docs/new-realtime-metrics-content, based on release/new-azion-docs at 688e99ac4.

The Real-Time Metrics Overview carried four kinds of page in one file: an overview, a 60-chart catalog built from 55 imported Help Center partials, an explanation of the Console controls, and a limits table. The Quickstart was a stub. The guides kept "How to" titles, and one targeted a GraphQL host that now answers 403. This PR rebuilds the section on the product section skeleton, in English and Portuguese.

• Section pages: a new Overview with a GraphQL specimen and a request-to-chart diagram, a tabbed Quickstart (Console and API), How it works, Limits, Best practices, Troubleshooting, and Glossary. Real-Time Metrics nests no Products, so the section has no dropdowns.
• Reference: the chart catalog becomes Build dashboards, Secure dashboards, and Observe dashboards, plus Filters and time range for the controls above the charts. The 55 partials are inlined into these pages and deleted. Their flow images become text, so the markdown twin carries them.
• Guides: the hub lists 11 guides, up from 6. Six are rewritten, three Grafana plugin guides join the hub and are rewritten, and three new tabbed guides cover status codes, cache offload, and the top sources of WAF threats. The two dashboard-JSON guides keep their JSON, and their data source moves to https://api.azion.com/v4/metrics/graphql.
• Retired: Historical Real-Time Metrics, a version discontinued at the end of 2024, and the "Use Real-Time Metrics" guide, whose content moves into the Quickstart. Both redirect.
• Verified: every API example ran against the live GraphQL API, read-only, and responses are anonymized. Console labels come from the public Console bundle. This corrects values the old pages carried: 37 selected fields, not 35; imagesProcessedMetrics; the time-range picker (initial Last 5 minutes, up to 730 days back); five Applications dashboards.
• Coverage: measured on the same frozen question set before and after, answered questions rose from 103 of 192 to 179 of 192.

**Related issue:**MM-16058
Pages affected: Real-Time Metrics, /documentation/platform/real-time-metrics/ and its pages (EN and PT); its guides under /documentation/guides/platform/observability/; src/nav/trees/real-time-metrics.json, src/nav/trees/guides.json, cicd/massive-redirect/. 144 files: 24 added (12 English, 12 Portuguese), 61 changed (30 English pages, 27 Portuguese, 4 nav and redirect files), 59 deleted (55 partials under src/includes/docs_help_center/en/real-time-metrics/, 4 retired pages).

Type of change

• 🆕 New content (feat)
• 🩹 Fix (fix) — typo, broken link, wrong information
• ♻️ Content update (docs) — rewrite, expansion, upkeep
• 🌐 Translation sync (i18n)
• 🏗️ Platform / structure (refactor / chore) — reviewed by UXE, no content mixed in — unticked: the nav and redirect changes ship with the pages that need them

Author checklist

• PR title follows type(scope): summary (see GOVERNANCE.md §4)
• Frontmatter complete: title, description, meta_tags, namespace, permalink, last_reviewed
• No legacy "edge-" product names in the copy
• How-to/tutorial content includes at least one runnable, copy-paste-tested code block
• Screenshots (if any) have alt text and follow image standards
• Internal links are relative and resolve locally
• If any permalink changed or page moved: redirect added in this PR
• i18n: pt-br updated in this PR or follow-up i18n
• I ran pnpm build:local (build + frontmatter check) without errors