docs: port upstream clickhouse-docs changes (26.4 changelog, dashboards, clickpipes)

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Summary

Ports the upstream clickhouse/clickhouse-docs merge commit a852961 from the Docusaurus repo into this Mintlify site.

Changes

• New v26.4 Cloud release-notes page added under resources/changelogs/cloud/release-notes/26_04.mdx, with sidebar_label/sidebar_position rewritten to sidebarTitle and added to release-notes-index.mdx and resources/changelogs/navigation.json.
• resources/changelogs/cloud/release-status.mdx — set 26.2 regular_end_date to 2026-06-17 and slow_start_date to 2026-07-01.
• resources/changelogs/cloud/2026.mdx — added the new "Note: horizontal and vertical autoscaling are mutually exclusive at GA" paragraph under Horizontal autoscaling.
• get-started/migrate/postgres/appendix.mdx — updated the Postgres → ClickHouse type map Nested link to the new anchor-less path.
• integrations/clickpipes/home.mdx — updated Google Cloud region eligibility language from "created on/before 27 May 2026" to "pre-existing ClickPipes prior to June 15th, 2026".
• integrations/clickpipes/{mysql,postgres}/parallel-initial-load.mdx — removed the obsolete NULL partition-key limitation bullet.
• integrations/connectors/data-ingestion/etl-tools/dbt/features-and-configurations.mdx — added the new reuse_connections profile setting.
• clickstack/features/dashboards/overview.mdx — renamed hyperdx-visualization-{1,2,3}.png references to clickstack-visualization-{1,2,3}.png, added the new clickstack-duplicate-series.png image and the "Duplicate series" paragraph.

Context

• Internal links converted to Mintlify root-relative paths where applicable.
• Docusaurus-only sidebar_position shuffles across the existing 24.x/25.x/26.2 release-notes were intentionally skipped — the Mintlify navigation order is controlled by resources/changelogs/navigation.json (already updated to put 26.4 first), so these frontmatter renumbers have no effect here.
• i18n/* updates from the upstream commit were ignored per the workflow rules.
• The new 26.4 release notes file is the upstream content verbatim — only the frontmatter (sidebar_label → sidebarTitle, sidebar_position dropped) was transformed for Mintlify.

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Note

Low Risk
Documentation-only edits (changelog, images, integration wording); no runtime or security-sensitive code paths.

Overview
Ports upstream clickhouse-docs changes into the Mintlify site, centered on a new v26.4 Cloud database release changelog (~800 lines) and wiring it into release-notes-index.mdx and navigation.json.

Cloud ops / product docs: release-status.mdx sets 26.2 regular_end_date to 2026-06-17 and slow_start_date to 2026-07-01. 2026.mdx adds that horizontal and vertical autoscaling are mutually exclusive at initial GA.

Integrations: ClickPipes static IP rules for Google Cloud now key off pre-existing ClickPipes before June 15, 2026 (replacing May 27 service-creation wording). MySQL/Postgres parallel initial load drops the NULL partition-key limitation bullet. dbt–ClickHouse docs add reuse_connections (default True) for multi-replica Cloud load balancing.

ClickStack dashboards: Chart Explorer screenshots switch hyperdx-visualization-* → clickstack-visualization-*, plus new copy and clickstack-duplicate-series.png for Duplicate series.

Minor: Postgres migration appendix Nested doc link; no application code changes.

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Project	Status	Preview	Updated (UTC)
ClickHouse-docs	🟢 Ready	View Preview	Jun 18, 2026, 3:13 PM