chore(apm): give bin a published description that describes it

Why: bin's marketplace description read "A place for things to be binned" — a
routing boundary sitting in the enumeration slot, phrased as a joke. It is what
a consumer sees in the marketplace listing for a plugin shipping eleven
substantive skills: research, write-docs, tdd, prototype, triage, diagnose,
improve-codebase-architecture, grill-me, grill-with-docs, zoom-out and caveman.

This is the same category error b0ef503 fixed for git and gitea, and the same
text bb9158d moved out of core's description in August — "triage, diagnosis,
architecture review" left core precisely because those skills live in bin, so
bin is where it should have landed.

Implementation notes: bin 1.1.3 -> 1.1.4, marketplace 0.4.3 -> 0.4.4, PATCH for
metadata under the per_package strategy. README's bin line mirrors the new
description. architecture.md's routing boundary is deliberately left as
"unsorted skills that have not earned a home yet" — that is still true, and it
answers a different question than the listing does.

Impact: consumer-facing. apm-pack-check-clean, check-plugin-content-sync,
check-marketplace-mirror-sync, validate-marketplace, validate-plugins and
apm-audit-ci all pass.

README.md

@@ -22,7 +22,7 @@ The six plugins:
 - **gitea** — issues, pull requests, labels, milestones, releases, branches, files
 - **core** — authoring and auditing a repo's `AGENTS.md` and the provider adapter files that defer to it
 - **lint** — configuring and running linters
-- **bin** — a place for things to be binned
+- **bin** — cross-cutting workflow skills not yet split into a focused plugin: research, documentation, TDD, prototyping, triage, diagnosis, architecture review, requirement grilling
 
 ## Prerequisites