feat(cli): add /gsd-sync-skills for cross-runtime managed skill sync (#2491)

* fix(tests): update 5 source-text tests to read config-schema.cjs

VALID_CONFIG_KEYS moved from config.cjs to config-schema.cjs in the
drift-prevention companion PR. Tests that read config.cjs source text
and checked for key literal includes() now point to the correct file.

Closes #2480

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* feat(cli): add /gsd-sync-skills for cross-runtime managed skill sync (#2380)

Adds /gsd-sync-skills command so multi-runtime users can keep gsd-* skill
directories aligned across runtime roots after updating one runtime with gsd-update.

Changes:
- bin/install.js: add --skills-root <runtime> flag that prints the skills root
  path for any supported runtime, reusing the existing getGlobalDir() table.
  Banner is suppressed when --skills-root is used (machine-readable output).
- commands/gsd/sync-skills.md: slash command definition
- get-shit-done/workflows/sync-skills.md: full workflow spec covering argument
  parsing, path resolution via --skills-root, diff computation (CREATE/UPDATE/
  REMOVE/SKIP), dry-run report (default), apply execution, idempotency guarantee,
  and safety rules (only gsd-* touched, dry-run performs no writes).

Safety rules: only gsd-* directories are ever created/updated/removed; non-GSD
skills in destination roots are never touched; --dry-run is the default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

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

docs/INVENTORY-MANIFEST.json

@@ -114,6 +114,7 @@
       "/gsd-ui-phase",
       "/gsd-ui-review",
       "/gsd-ultraplan-phase",
+      "/gsd-sync-skills",
       "/gsd-undo",
       "/gsd-update",
       "/gsd-validate-phase",
@@ -192,6 +193,7 @@
       "spike-wrap-up.md",
       "spike.md",
       "stats.md",
+      "sync-skills.md",
       "transition.md",
       "ui-phase.md",
       "ui-review.md",

docs/INVENTORY.md

@@ -54,7 +54,7 @@ Full roster at `agents/gsd-*.md`. The "Primary doc" column flags whether [`docs/
 
 ---
 
-## Commands (82 shipped)
+## Commands (83 shipped)
 
 Full roster at `commands/gsd/*.md`. The groupings below mirror `docs/COMMANDS.md` section order; each row carries the command name, a one-line role derived from the command's frontmatter `description:`, and a link to the source file. `tests/command-count-sync.test.cjs` locks the count against the filesystem.
 
@@ -165,6 +165,7 @@ Full roster at `commands/gsd/*.md`. The groupings below mirror `docs/COMMANDS.md
 | `/gsd-settings` | Configure GSD workflow toggles and model profile. | [commands/gsd/settings.md](../commands/gsd/settings.md) |
 | `/gsd-set-profile` | Switch model profile for GSD agents (quality/balanced/budget/inherit). | [commands/gsd/set-profile.md](../commands/gsd/set-profile.md) |
 | `/gsd-pr-branch` | Create a clean PR branch by filtering out `.planning/` commits. | [commands/gsd/pr-branch.md](../commands/gsd/pr-branch.md) |
+| `/gsd-sync-skills` | Sync managed GSD skill directories across runtime roots for multi-runtime users. | [commands/gsd/sync-skills.md](../commands/gsd/sync-skills.md) |
 | `/gsd-update` | Update GSD to latest version with changelog display. | [commands/gsd/update.md](../commands/gsd/update.md) |
 | `/gsd-reapply-patches` | Reapply local modifications after a GSD update. | [commands/gsd/reapply-patches.md](../commands/gsd/reapply-patches.md) |
 | `/gsd-help` | Show available GSD commands and usage guide. | [commands/gsd/help.md](../commands/gsd/help.md) |
@@ -249,6 +250,7 @@ Full roster at `get-shit-done/workflows/*.md`. Workflows are thin orchestrators
 | `spike.md` | Rapid feasibility validation through focused, throwaway experiments. | `/gsd-spike` |
 | `spike-wrap-up.md` | Curate spike findings and package them as a persistent `spike-findings-[project]` skill. | `/gsd-spike-wrap-up` |
 | `stats.md` | Project statistics rendering — phases, plans, requirements, git metrics. | `/gsd-stats` |
+| `sync-skills.md` | Cross-runtime GSD skill sync — diff and apply `gsd-*` skill directories across runtime roots. | `/gsd-sync-skills` |
 | `transition.md` | Phase-boundary transition workflow — workstream checks, state advancement. | `execute-phase.md`, `/gsd-next` |
 | `ui-phase.md` | Generate UI-SPEC.md design contract via gsd-ui-researcher. | `/gsd-ui-phase` |
 | `ui-review.md` | Retroactive 6-pillar visual audit via gsd-ui-auditor. | `/gsd-ui-review` |