* test(#2941): add regression for bare-skill-name global: hint
When a bare skill name matches an existing global skill, the skip warning
must hint at the global: prefix. When no global skill matches, the original
'Skill not found' warning is unchanged.
* fix(#2941): hint at global: prefix when a bare skill name matches a global skill
When buildAgentSkillsBlock skips a bare skill name that doesn't exist as a
project-relative path, check if it matches an existing global skill. If so,
append a hint to the warning: 'a global skill named X exists; use global:X
to reference it'. When no global skill matches, the warning is unchanged.
getGlobalSkillDir and getGlobalSkillsBase are already imported in this module
for the global: branch. The hint is guarded on globalSkillsBase being non-null
(runtimes without a skills directory don't support the prefix).
* chore(#2941): add changeset fragment
* chore(#2941): backfill changeset PR number 2973
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Co-authored-by: sim <sim@local>
