#611 Guide users toward filing feature requests when @swamp extensions lack a needed capability

Problem

When a user (or coding agent) works with an official @swamp/* extension and discovers it lacks a method or capability they need, there is no nudge from the CLI pointing them at the feedback channel. The typical outcome is a workaround: wrapping the CLI in shell scripts, building a redundant custom extension, or abandoning the official extension entirely. The publisher never learns about the gap, so the extension never improves.

Proposed solution

Have swamp actively guide users toward swamp issue feature --extension @swamp/<name> at the moments a capability gap becomes visible:

• When swamp model method run is invoked with a method that does not exist on the type, the error message should suggest filing a feature request against the extension (in addition to listing available methods).
• swamp model type describe output could include a one-line footer noting how to request missing functionality for the extension that provides the type.
• Agent-facing guidance (skill docs / templates shipped with extensions) should instruct agents to file an extension-scoped feature request before falling back to custom extension models or shell workarounds.

Scope / affected components

• Method-resolution error path in the CLI (unknown-method error rendering)
• model type describe output rendering
• Issue/extension skill documentation shipped to agents

Alternatives considered

• Documentation-only change (mention in extension README templates) — lower friction but unlikely to be seen at the moment the gap is hit.
• Leaving it to publishers to solicit feedback — does not help with the common case where the user silently works around the gap.