refactor(#1289): T5 — migrate the final idiom-hard callers off the core spine (#1290)

The last 4 core importers, migrated off non-destructure idioms:
- gsd-tools.cjs: core.{error,ERROR_REASON,setJsonErrorMode,output} -> io.cjs;
  core.findProjectRoot -> project-root.cjs (lazy wrapper preserved); inline
  resolveWorktreeRoot require -> worktree-safety.cjs
- audit-command-router: DI default `_core ?? core` -> `_core ?? io` (seam preserved)
- intel-command-router: DI default -> `{ output: io.output, timeAgo: coreUtils.timeAgo }` (seam preserved)
- check-command-router: io destructure -> io.cjs; dynamic core['planningDir']
  -> planning-workspace, core['findPhaseInternal'] -> phase-locator (typed
  imports, dropped the Record-cast bracket hack)

Allowlist is now EMPTY — NO file imports the core spine. core.cts re-exports
are dead weight; T-final deletes core.cts + remaining shim tests + the lint.
No behaviour change.

Closes #1289

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/intel-command-router.cts

@@ -38,14 +38,17 @@
  * the case block).
  */
 
-// eslint-disable-next-line @typescript-eslint/no-require-imports
-import core = require('./core.cjs');
 // eslint-disable-next-line @typescript-eslint/no-require-imports
 import io = require('./io.cjs');
 // eslint-disable-next-line @typescript-eslint/no-require-imports
+import coreUtils = require('./core-utils.cjs');
+// eslint-disable-next-line @typescript-eslint/no-require-imports
 import path = require('path');
 
 const { ERROR_REASON } = io;
+// Default CoreModule implementation assembled from leaf modules.
+// _core seam overrides this entirely for test injection.
+const _defaultCore = { output: io.output, timeAgo: coreUtils.timeAgo };
 
 // ─── Types ────────────────────────────────────────────────────────────────────
 
@@ -83,7 +86,7 @@ interface RouteIntelCommandOptions {
 function routeIntelCommand({ args, cwd, raw, error, _intel, _core }: RouteIntelCommandOptions): void {
   // eslint-disable-next-line @typescript-eslint/no-require-imports, @typescript-eslint/no-unsafe-assignment
   const intel: IntelModule = _intel ?? require('./intel.cjs');
-  const c: CoreModule = _core ?? core;
+  const c: CoreModule = _core ?? _defaultCore;
   const subcommand = args[1];
 
   if (subcommand === 'query') {