test: regression suite + E2E for v1.27.0.0 rename

Three new regression tests guard the rename's blast radius (per codex
Findings #1, #8, #9, #12):

- test/no-stale-gstack-brain-refs.test.ts: greps bin/, scripts/, *.tmpl,
  test/ for forbidden identifiers (gstack-brain-init, gbrain_sync_mode);
  fails CI if any non-allowlisted file references them.
- test/post-rename-doc-regen.test.ts: confirms gen-skill-docs output has
  no stale references in any */SKILL.md (the cross-product blind spot).
- test/setup-gbrain-path4-structure.test.ts: structural lint over the
  Path 4 prose contract — STOP gates after verify failure, never-write-
  token rules, mode-aware CLAUDE.md block, bearer always via env-var.

Two new gate-tier E2E tests (deterministic stub HTTP server, fixed inputs):

- test/skill-e2e-setup-gbrain-remote.test.ts: Path 4 happy path. Stubs
  an HTTP MCP server, drives the skill via Agent SDK with a stubbed
  bearer, asserts claude.json gets the http MCP entry, CLAUDE.md gets
  the remote-http block, the secret token NEVER leaks to CLAUDE.md.
- test/skill-e2e-setup-gbrain-bad-token.test.ts: stub server returns 401;
  asserts the AUTH classifier hint surfaces, no MCP registration occurs,
  CLAUDE.md is unchanged. Regression guard for the "verify failed → STOP"
  rule.

touchfiles.ts: setup-gbrain-remote and setup-gbrain-bad-token added at
gate-tier so CI catches Path 4 regressions on every PR.

Plus a few comment refs flipped: bin/gstack-jsonl-merge, bin/gstack-timeline-log
(legacy gstack-brain-init mentions in headers).

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

bin/gstack-timeline-log

@@ -4,7 +4,7 @@
 #
 # Session timeline: local by default. If the user enables `artifacts_sync_mode`
 # with the `full` (not `artifacts-only`) privacy tier — via the first-run
-# stop-gate from `gstack-brain-init` or the preamble — timeline events are
+# stop-gate from `gstack-artifacts-init` or the preamble — timeline events are
 # published to the user's private GBrain sync repo. See docs/gbrain-sync.md.
 # Required fields: skill, event (started|completed).
 # Optional: branch, outcome, duration_s, session, ts.