Serve plugin discovery and listing workflows

[brsbl]

Product intent and requirements

• Make the server the single owner of plugin category, catalog, listing, health, and compatibility policy.
• Read additive marketplace v2 metadata while retaining v1 fallback for released clients and registries.
• Expose plugin listing, screenshot, update, and submission workflows through both the CLI and agent skills—not UI-only actions.
• Provide consistent official-plugin metadata and screenshot assets for downstream Browse and detail surfaces.

What was wrong

The server and CLI could not yet publish the discovery contracts as product behavior: category assignment was fragmented, authored listing state had no routes, screenshot capture did not register end to end, and the catalog reader only understood the released v1 marketplace shape.

What changed

• Adds the server category registry, v2 catalog parsing with v1 fallback, listing lifecycle service/routes, runtime health history, and catalog metadata projection.
• Adds bb plugin screenshot and listing/update command output, including desktop capture support.
• Updates the bb CLI, submission, and screenshot skills plus their discoverable references.
• Adds official screenshot assets used by bundled-plugin listings.
• Locks compatibility to the released strict v1 parser fixture; the host-daemon protocol is unchanged.

Product context

This service and CLI layer supplies the catalog metadata and exact screenshot assets used by downstream public and in-app discovery surfaces; it does not itself change app UI.

## How you verified

• This is a service/CLI layer with no app UI change, so UI screenshot evidence is not applicable.
• Pull-request CI is green on exact head 7416f20621066f378a784b1e7443b68eb34bd902; all required checks passed and the platform-inapplicable jobs were skipped.
• No CI-equivalent tests, typechecks, or lint were run locally per repository policy. Pull-request CI is the validation path.

BB-Thread-ID: thr_9tmqez22hd

AGENT GENERATED

[SawyerHood]

Closing: the server and CLI work landed in a rebuilt form in #2880 (v2 parser, category resolution, CLI search column, guide updates) and #2892 (the bundled bb-official marketplace replaces the hardcoded builtin catalog merge). The listing lifecycle and screenshot capture were dropped by owner decision.

AGENT GENERATED