feat(skills): default user-invocable to true

[CnsMaple]

Summary

• Make user-invocable opt-out: when a SKILL.md does not declare the field, the skill appears in the command palette by default.
• Skills that should stay hidden from the palette can opt out explicitly with user-invocable: false.
• Switches Skill.UserInvocable to *bool so the catalog layer can tell "absent" from "false" without parsing YAML twice; downstream CatalogEntry / SkillInfo keep a plain bool filled in from a new Skill.IsUserInvocable() helper, so no consumer changes are required.
• Adds table-driven coverage in internal/skills/skills_test.go for the absent / true / false cases.

Motivation

The user-invocable feature (#2834) currently requires every skill author to add user-invocable: true to opt in. In practice most custom skills are workflow shortcuts the user wants to fire from the command palette, so the friction is mostly on the common case. Flipping the default makes the feature useful out of the box while still allowing explicit opt-out for skills that are meant to be model-only (especially in combination with disable-model-invocation: true).

Related

• feat(skills): add support for user invocable skills #2834 — initial user-invocable frontmatter support
• feat(skills): add description to skill picker & use attachements #2970 — description + attachment style in the skill picker
• feat(skills): add dialog to command palette #2562 / feat(skills): add dialog to command palette #2467 — earlier command-palette dialogs that this implementation effectively replaces for skill invocation
• Improvements to the Skills feature (knowing what skills it has) #1972 — broader discussion on skill discoverability / forced invocation

Test plan

• go test ./internal/skills/... — new TestIsUserInvocable_DefaultTrue covers absent / true / false
• go test ./internal/commands/... — TestFromSkillCatalog_UserInvocableOnly and symlink test still pass
• go build ./... clean

Note

This change was authored with AI assistance (Crush / MiniMax-M3) and should be reviewed carefully. The semantic change is small (a single default flip) but it affects every skill in the system, so the explicit opt-out path should be documented once the PR is approved.

Supersedes the head ref of the originally opened PR (#3079) which closed automatically when the source branch was renamed.

💘 Generated with Crush

Assisted-by: Crush:MiniMax-M3

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