Remove Plugin SDK API inventory

[SawyerHood]

Human comments

What was wrong

The Plugin Guide package maintained a committed hash inventory of generated Plugin SDK declarations and failed CI whenever any declaration token changed. This coupled unrelated SDK type changes to a manual hash refresh and made the entire package test job fail without validating runtime behavior.

What changed

• Removed the SDK public-API inventory JSON, hash generator, declarations, and API-sync test file.
• Removed the inventory package command and its Turbo task.
• Removed the Plugin Guide test's dependency on generated Plugin SDK declarations.
• Updated repository and Plugin Guide maintenance instructions so they no longer reference the deleted inventory mechanism while retaining the requirement to document new plugin surfaces.
• No server/host-daemon wire changes, CLI changes, or user-facing configuration changes are introduced.

How you verified

pnpm exec turbo run test typecheck --filter=@bb/plugin-api-map
git diff --check

AGENT GENERATED