feat(#787): elevate Cline — .clinerules/ dir form, PreToolUse hook, AGENTS.md (#803)

* feat(#787): elevate Cline — .clinerules/ dir form, PreToolUse hook, AGENTS.md

Migrate the installer's Cline output from a single-file .clinerules to the
.clinerules/ directory form (.clinerules/gsd.md), which is the prerequisite for
Cline's v3.36 hooks (a path cannot be both a file and a directory). Add a
.clinerules/hooks/PreToolUse lifecycle hook implementing Cline's JSON stdin ->
{cancel,errorMessage,contextModification} protocol; it guards .planning/
artifacts and fails open. On global installs, merge GSD instructions into the
cross-tool ~/.agents/AGENTS.md target (marker-delimited, merge-safe). A legacy
single-file .clinerules is migrated in place; --uninstall removes the new
artifacts and strips the AGENTS.md GSD block.

Also fixes the uninstall targetDir for Cline local installs (it pointed at
./.cline instead of the project root) and re-runs writeManifest after the
Cline artifacts are written so they are hash-tracked.

Self-contained: implemented independently of the #782 Cline skills work.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(#787): address review findings

- Scope PreToolUse hook path-walk to PATH_KEY fields only (eliminates false
  positive when doc body content mentions .planning/)
- Use lstatSync + isSymbolicLink() for migration guard so GSD never writes
  through a user's symlinked .clinerules into an external directory
- Add regression tests for both cases

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

* chore(#787): set changeset pr: 803

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

---------

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

tests/installer-migration-install-integration.test.cjs

@@ -232,10 +232,11 @@ function assertFreshInstallContract(runtime, targetDir) {
       `${runtime} should install commands/gsd entries`
     );
   } else if (contract.surface === 'clinerules') {
+    // #787: Cline now uses the .clinerules/ directory form (rules at gsd.md).
     assert.match(
-      fs.readFileSync(path.join(targetDir, '.clinerules'), 'utf8'),
+      fs.readFileSync(path.join(targetDir, '.clinerules', 'gsd.md'), 'utf8'),
       /GSD workflows live in `gsd-core\/workflows\/`/,
-      'Cline should install root .clinerules guidance'
+      'Cline should install .clinerules/gsd.md guidance'
     );
   }