Plugin Docs CLI: Always sort root index.md first in manifest

[sunker]

What this PR does / why we need it:

When a plugin is packaged, @grafana/plugin-docs-cli runs a build step that scans the docs folder and generates a manifest.json describing the page tree. Pages are sorted by sidebar_position frontmatter, with files that don't set it falling back to Infinity, sorting them last.

The root index.md (the landing page) has no special sort treatment, so plugin authors who omit sidebar_position end up with their overview page at the bottom of the nav on grafana.com (as shown in the screenshot below, where the overview is missing from the top of the docs nav). The fix gives index.md implicit first-place priority in the sort, without requiring authors to set sidebar_position manually.

Before	After

Which issue(s) this PR fixes:

Special notes for your reviewer:

📦 Published PR as canary version: Canary Versions

✨ Test out this PR locally via:

npm install website@5.6.1-canary.2636.26226198477.0
npm install @grafana/create-plugin@7.6.1-canary.2636.26226198477.0
npm install @grafana/plugin-docs-cli@0.0.11-canary.2636.26226198477.0
npm install @grafana/plugin-meta-extractor@0.12.3-canary.2636.26226198477.0
# or 
yarn add website@5.6.1-canary.2636.26226198477.0
yarn add @grafana/create-plugin@7.6.1-canary.2636.26226198477.0
yarn add @grafana/plugin-docs-cli@0.0.11-canary.2636.26226198477.0
yarn add @grafana/plugin-meta-extractor@0.12.3-canary.2636.26226198477.0

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[Copilot]

Pull request overview

This PR updates @grafana/plugin-docs-cli’s manifest generation so that a root-level index.md (the landing/overview page) is always sorted first in the generated manifest.json, even when sidebar_position is omitted. This prevents the overview page from being pushed to the bottom of the docs nav when authors rely on default ordering.

Changes:

• Update page sorting to always prioritize root index.md ahead of sidebar_position ordering.
• Add a regression test fixture and test case covering “no sidebar_position on root index”.
• Introduce new docs fixtures to validate the corrected ordering behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/plugin-docs-cli/src/scanner.ts	Adjusts sorting comparator to place root index.md first before applying sidebar_position ordering.
packages/plugin-docs-cli/src/scanner.test.ts	Adds test ensuring root index.md is the first manifest page when it has no sidebar_position.
packages/plugin-docs-cli/src/fixtures/no-position-index-docs/index.md	New fixture root index page without sidebar_position.
packages/plugin-docs-cli/src/fixtures/no-position-index-docs/guide.md	New fixture page with sidebar_position to ensure index still sorts first.