chore: consume the shared component from the shared/ folder on main

[JakeSCahill]

What this does

Points this playbook at the shared component's new home. The component is moving from the dedicated shared branch of redpanda-data/docs to a shared/ folder on main, so this:

• drops shared from the branches list of the redpanda-data/docs source
• adds the folder as its own content source with start_path: shared

Same shape as redpanda-data/docs#1892 and redpanda-data/rp-connect-docs#485.

⚠️ Do not merge before redpanda-data/docs#1892

The shared/ folder does not exist on docs main until #1892 lands. Merging this first points the playbook at a folder that isn't there, and the playbook loses the shared component entirely — no glossary terms, no enterprise features registry.

Why this matters

This is a local playbook, so the published site is unaffected either way — the production cutover is docs-site#205. The cost of not doing this is that local previews in this repo silently lose the shared component once the shared branch is retired, which is easy to misread as a content bug.

Conversely, leaving any consumer on the branch means the shared branch can't be retired, and the folder and branch keep drifting. That drift already bit docs#1892: four glossary terms in the folder copy still carried the old ADP acronym after #1894 updated the branch.

Verification

• YAML parses
• no shared entry remains in the docs source's branches
• exactly one source with start_path: shared

🤖 Generated with Claude Code