fix(3584): runtime-aware slash formatter for user-facing emissions

Introduce `runtime-slash.cjs` as the single source of truth for emitting
GSD slash-command references in user-facing runtime output and persisted
artifacts. `formatGsdSlash(commandName, runtime)` produces `/gsd-<cmd>`
for skills-based runtimes (Claude/Cursor/OpenCode/Kilo/etc.) and
`$gsd-<cmd>` for Codex. The deprecated `/gsd:<cmd>` colon form is never
emitted — pasting a recommended-action command into Claude Code now
routes correctly instead of failing with `Unknown command`.

Wired into the high-impact emitters identified in #3584:

- `init.cjs` `cmdInitManager` recommended_actions[].command (the
  original failure path in the bug report) plus the no-ROADMAP /
  no-STATE error hints.
- `phase.cjs` `cmdPhaseAdd`, `cmdPhaseAddBatch`, `cmdPhaseInsert` —
  ROADMAP.md `Plans:` references now persist the routable form
  instead of the legacy colon form.
- `verify.cjs` `cmdValidateHealth` — every fix-hint addIssue() call
  (E001/E002/E003/E004/E005, W002/W003/W008/W009/W011/W016/W018) and
  the persisted STATE.md regenerate / MILESTONES.md backfill notes.
- `milestone.cjs` `cmdMilestoneComplete` — Operator Next Steps tail
  rewrite.
- `validate-command-router.cjs` — `validate context` recommendation
  strings for WARNING/CRITICAL utilization bands.
- `workstream.cjs` — missing .planning hint.
- `profile-output.cjs` — `generate-claude-md` workflow enforcement
  block, project/skills fallbacks, profile placeholder, and the
  dev-preferences refresh hints.
- `drift.cjs`, `gsd2-import.cjs`, `commands.cjs scaffold context` —
  remaining one-off persisted references.

Runtime detection: `resolveRuntime(projectDir)` reads
`process.env.GSD_RUNTIME` first, then a side-effect-free direct read of
`.planning/config.json` (NOT `loadConfig`, which would normalize legacy
keys and re-write the file just to read the runtime name).

Tests:
- `tests/bug-3584-runtime-slash-formatter.test.cjs` — 22 unit tests
  covering the pure formatter and resolver (hyphen vs codex, prefix
  normalization, defensive returns, env/config/default chain).
- `tests/bug-3584-runtime-slash-emitters.test.cjs` — 6 integration
  tests exercising `init manager`, `phase add` (via the structured
  `roadmap get-phase` payload to avoid raw-text matching on the
  on-disk artifact), `validate health`, `validate context`, and the
  codex variant.
- Existing tests updated to assert the new contract: validate-context
  recommendations, claude-md workflow block, milestone complete
  Operator Next Steps. Copilot-install engine-conversion test now
  asserts against a synthetic input since bin/lib/*.cjs no longer
  contains literal `/gsd:` references for the install-time converter
  to rewrite.

INVENTORY.md and INVENTORY-MANIFEST.json updated for the new module
(64 CLI modules shipped, +1).

Fixes #3584

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

tests/milestone.test.cjs

@@ -244,7 +244,9 @@ describe('milestone complete command', () => {
     assert.ok(state.includes('Phase: Milestone v1.0 complete'));
     assert.ok(state.includes('Status: Awaiting next milestone'));
     assert.ok(!state.includes('Re-run /gsd:complete-milestone'));
-    assert.ok(state.includes('/gsd:new-milestone'));
+    // #3584: persisted ROADMAP/STATE strings now use the runtime-routable
+    // hyphen-form slash command (formatter resolves codex → $gsd-, others → /gsd-).
+    assert.ok(state.includes('/gsd-new-milestone'));
   });
 
   test('appends canonical narrative sections when STATE.md headings are missing (#3088)', () => {
@@ -261,7 +263,8 @@ describe('milestone complete command', () => {
     assert.ok(state.includes('## Current Position'));
     assert.ok(state.includes('Phase: Milestone v1.0 complete'));
     assert.ok(state.includes('## Operator Next Steps'));
-    assert.ok(state.includes('/gsd:new-milestone'));
+    // #3584: hyphen form is the runtime-routable shape for skills-based installs.
+    assert.ok(state.includes('/gsd-new-milestone'));
   });
 
   test('handles missing ROADMAP.md gracefully', () => {