Add optional bugs field to the plugin manifest (issue tracker URL)

[unional]

Problem. plugin.json has homepage and repository but no way to say where users or tooling should report problems with the plugin. repository is not a reliable substitute: the tracker is not necessarily at the repository URL, because it may be a separate project-management tool, a different host, or a shared tracker for several plugins. Today a plugin that needs this has to put it in a client-specific extensions namespace, so each client invents its own key.

Who hits it. Plugin authors who track work outside the repo. Tooling that wants to route a problem to the right place, such as a skill that drafts a bug report when it detects a configuration gap in the plugin it ships with.

Why the portable spec. It is pure metadata with no client behavior, like homepage and repository. A shared key lets tools and registries read it without knowing each other's namespaces.

Proposal. An optional top-level bugs, mirroring npm's package.json: a URL string, or an object with optional url and email. Clients assign no behavior to it beyond display.

Prior art. npm package.json bugs. Python's Project-URL: Bug Tracker. Cargo has no direct equivalent, since it relies on repository.

Implementer interest. I don't know of specific implementers, but all clients should support it. It is a well-established design in the JavaScript ecosystem.