fix(#2543): replace legacy /gsd-<cmd> syntax with /gsd:<cmd> across all source files (#2595)

Commands are now installed as commands/gsd/<name>.md and invoked as
/gsd:<name> in Claude Code. The old hyphen form /gsd-<name> was still
hardcoded in hundreds of places across workflows, references, templates,
lib modules, and command files — causing "Unknown command" errors
whenever GSD suggested a command to the user.

Replace all /gsd-<cmd> occurrences where <cmd> is a known command name
(derived at runtime from commands/gsd/*.md) using a targeted Node.js
script. Agent names, tool names (gsd-sdk, gsd-tools), directory names,
and path fragments are not touched.

Adds regression test tests/bug-2543-gsd-slash-namespace.test.cjs that
enforces zero legacy occurrences going forward. Removes inverted
tests/stale-colon-refs.test.cjs (bug #1748) which enforced the now-obsolete
hyphen form; the new bug-2543 test supersedes it. Updates 5 assertion
tests that hardcoded the old hyphen form to accept the new colon form.

Closes #2543

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

get-shit-done/workflows/map-codebase.md

@@ -365,12 +365,12 @@ Created .planning/codebase/:
 
 `/clear` then:
 
-`/gsd-new-project`
+`/gsd:new-project`
 
 ---
 
 **Also available:**
-- Re-run mapping: `/gsd-map-codebase`
+- Re-run mapping: `/gsd:map-codebase`
 - Review specific file: `cat .planning/codebase/STACK.md`
 - Edit any document before proceeding