fix(#2697): replace retired /gsd: prefix with /gsd- in all user-facing text (#2699)

All workflow, command, reference, template, and tool-output files that
surfaced /gsd:<cmd> as a user-typed slash command have been updated to
use /gsd-<cmd>, matching the Claude Code skill directory name.

Closes #2697

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

get-shit-done/workflows/execute-phase/steps/codebase-drift-gate.md

@@ -34,7 +34,7 @@ New migrations:
 New route modules:
   - {path}
 
-Run /gsd:map-codebase --paths {affected_paths} to refresh planning context.
+Run /gsd-map-codebase --paths {affected_paths} to refresh planning context.
 ```
 
 Then continue to `verify_phase_goal`. Do NOT block. Do NOT spawn anything.