#610 Guide users toward filing feature requests when @swamp extensions are missing features

Problem

When a user works with an official @swamp/* extension that covers their domain but lacks a needed method or capability, nothing in the CLI or agent-facing guidance nudges them to file a feature request upstream. The current guidance steers users toward extending the type locally or building a custom extension model. The result: useful feature gaps never reach the extension maintainers, and users accumulate local workarounds that duplicate work across repos.

Proposed solution

Have swamp actively guide users toward swamp issue feature --extension @swamp/<name> when a capability gap in an official extension is detected. Possible touchpoints:

• Agent skill guidance (model/extension skills): when the recommended path is 'extend an existing @swamp/* type because it lacks a method', also instruct the agent to offer filing a feature request against that extension.
• CLI hints: e.g. after swamp model type describe or a failed method lookup on an @swamp/* type, print a hint pointing at swamp issue feature --extension <name>.
• Docs/templates: mention the extension-scoped feature flow in the extension authoring/extending guidance.

Local extension remains the immediate unblock; the upstream feature request should be the encouraged parallel step so maintainers learn about real demand.

Alternatives considered

• Status quo: users extend locally and gaps stay invisible to publishers.
• Manual process documentation only (per-repo CLAUDE.md rules): doesn't scale across repos and is easy to miss.