Extend the affordance overlay (per-command --help guidance) beyond
generated service-API methods to +-prefixed shortcuts, and let a command
point at specific related skills.
- shortcuts render the same guidance block as methods, from `## +cmd`
entries in affordance/<domain>.md; the lookup coordinate is unified in
cmdmeta (SetAffordanceRef/AffordanceRef) so both share one path
- PrepareShortcutHelp composes onto the command's captured base, so a
shortcut's PostMount-authored Long (e.g. the docs "read the skill"
directive) is preserved, not clobbered
- a per-command `### Skills` section merges with the domain `> skill:`
default (deduped, domain first); an entry may be a bare skill name or a
name/relpath reference (lark-contact/references/x.md), validated against
the embedded skill tree and dropped when unresolved
- +-prefixed headings resolve verbatim (no space->dot folding)
- guide contact's +search-user / +get-user shortcuts, dropping the
+search-user Go tips now covered by the overlay's examples and lead
Tips precedence: a shortcut's overlay `### Tips` replace its Go Tips field.