fix(#2808): SKILL.md files use hyphen name form (gsd-cmd not gsd:cmd) (#2819)

* fix(#2808): SKILL.md name uses hyphen form for Claude Code autocomplete

skillFrontmatterName() was converting gsd-<cmd> to gsd:<cmd> (colon) so
installed SKILL.md files had name: gsd:add-phase etc. Claude Code surfaces
this name in autocomplete, showing the deprecated colon form to users even
though the hyphen form is canonical everywhere else.

Root cause: the colon form was needed because workflows called
Skill(skill="gsd:<cmd>"). All 4 remaining colon-form Skill() calls in
autonomous.md and execute-phase.md are updated to hyphen form.

skillFrontmatterName() now returns the hyphen dir name unchanged.
Updated 4 existing tests that asserted colon form.

Regression test: tests/bug-2808-skill-hyphen-name.test.cjs

* fix(#2808): address CodeRabbit — bash/text fences, structured test assertions, fail-loud on errors

get-shit-done/workflows/execute-phase.md

@@ -1095,7 +1095,7 @@ If `CODE_REVIEW_ENABLED` is `"false"`: display "Code review skipped (workflow.co
 
 **Invoke review:**
 ```
-Skill(skill="gsd:code-review", args="${PHASE_NUMBER}")
+Skill(skill="gsd-code-review", args="${PHASE_NUMBER}")
 ```
 
 **Check results using deterministic path (not glob):**