test: add run-tests.sh, fix stale tests for marketplace model

- Add tests/run-tests.sh: discovers and runs all test-*.sh (including
  plugin subdirs) and the bats suite; replaces per-script pre-push calls
- Add tests/run-tests.bats: TDD coverage for run-tests.sh behaviours
- Update setup-hooks.sh: pre-push block now calls run-tests.sh
- Fix test-install.sh: remove provider adapter symlink tests (adapter
  removed in marketplace migration), guard skills loops on dir existence
- Fix test-instructions-and-docs.sh: content index checks now point to
  core/AGENTS.md (where it lives), remove ard/bug dir assertions
- Fix test-setup-hooks.sh: assert pre-push hook calls run-tests.sh

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

scripts/setup-hooks.sh

@@ -197,11 +197,7 @@ pre_push_block() {
 HOOKS_SCRIPT_DIR="$script_dir"
 REPO_ROOT="\$(git rev-parse --show-toplevel)"
 
-echo "Running test suite..."
-bash "\$REPO_ROOT/tests/test-install.sh"
-bash "\$REPO_ROOT/tests/test-governance-layer.sh"
-bash "\$REPO_ROOT/tests/test-check-manifests.sh"
-bash "\$REPO_ROOT/tests/test-setup-hooks.sh"
+bash "\$REPO_ROOT/tests/run-tests.sh"
 
 echo "Checking manifests..."
 bash "\$HOOKS_SCRIPT_DIR/check-manifests.sh" "\$REPO_ROOT"