release-25.2: ui/cluster-ui: add optional headers to jobs/databases pages

[janmorales7]

Informs: CNSL-2186

Backport 1/1 commits from #169819.

/cc @cockroachdb/release

• Non-production code changes OR fixes for serious issues. Non-production includes test-only changes, build system changes, etc. Serious issues are defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to. Reference the approved ENGREQ ticket in the PR body (e.g., "Fixes ENGREQ-123").

---

Make the page header optional via a showHeader prop on both JobsPage and DatabasesPageV2, allowing parent components to suppress the heading when embedding these pages in other layouts.

Move the "Auto stats collection" toggle from the PageHeader actions slot into the PageConfig filter bar on the databases page so it sits alongside other page-level controls.

A local stylesheet (databasesPageRoot.module.scss) is introduced to add margin-top: 10px on the content section below PageConfig. This compensates for the shared PageConfig container's margin-bottom: -10px (a sticky-header spacing trick) without modifying the shared stylesheet that affects 16+ pages.

Release justification: UI-only changes for embedded page support - no user-facing functionality changes, just optional prop for embedded layouts.

[trunk-io]

Merging to release-25.2 in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes OR fixes for serious issues. Non-production includes test-only changes, build system changes, etc. Serious issues are defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to. Reference the approved ENGREQ ticket in the PR body (e.g., "Fixes ENGREQ-123").

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[cockroach-teamcity]

This change is 

[blathers-crl]

❌ PR #169867 does not comply with backport policy

Confidence: high
Explanation: The pull request involves changes to UI files within pkg/ui/workspaces/cluster-ui/ which are classified as production code under the CockroachDB Backport Policy. The PR does not meet the critical bug criteria, as the changes pertain to UI adjustments (making headers optional and relocating a toggle) rather than addressing stability, security issues, data corruption/loss, significant performance regressions, bugs causing incorrect results or suboptimal performance, or improving debugging capabilities. The PR includes a 'Release justification:' line, but the justification 'Add optional header support for embedded pages' does not meet the standards for an exception under the policy, since it does not address a critical issue or describe why the change is necessary for the backport other than UI customization. The feature flag policy is not applicable here as no new feature flags or cluster settings are introduced that control the behavior of new features.
Recommendation: Reconsider the backport or provide a stronger justification for why this change is critical and should be backported. Alternatively, structure this deployment behind a feature flag if it introduces new functionality.

✅ ENGREQ Check Passed: No ENGREQ required (non-production code or serious issues).

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}