docs: update project documentation for v1.80.0.0

README troubleshooting + manual uninstall cover the skill ownership gate
(.gstack-owned marker, ~/.gstack/backups/skills/<ts>/, foreign same-name
skills left untouched). CLAUDE.md and CONTRIBUTING carry the ownership and
best-effort Chromium bootstrap invariants for people editing setup and
gstack-relink. PROJECT_STRUCTURE gains careful/, freeze/, guard/, unfreeze/,
gstack-upgrade/, gstack-relink, and the setup/relink/hook test files.
TESTING_INTERNALS documents the anchor-sliced setup harness convention.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/PROJECT_STRUCTURE.md

@@ -36,6 +36,7 @@ gstack/
 │   ├── fixtures/    # Ground truth JSON, planted-bug fixtures, eval baselines
 │   ├── skill-validation.test.ts  # Tier 1: static validation (free, <1s)
 │   ├── gen-skill-docs.test.ts    # Tier 1: generator quality (free, <1s)
+│   ├── setup-*.test.ts, relink.test.ts, hook-scripts.test.ts  # Tier 1: setup linker ownership + Chromium bootstrap (anchor-sliced from setup), gstack-relink, PreToolUse hooks (free)
 │   ├── skill-llm-eval.test.ts   # Tier 3: LLM-as-judge (~$0.15/run)
 │   └── skill-e2e-*.test.ts       # Tier 2: E2E via claude -p (~$3.85/run, split by category)
 ├── qa-only/         # /qa-only skill (report-only QA, no fixes)
@@ -54,7 +55,11 @@ gstack/
 ├── investigate/     # /investigate skill (systematic root-cause debugging)
 ├── spec/            # /spec skill (five-phase spec → GitHub issue, optional agent spawn, /ship auto-closes)
 ├── retro/           # Retrospective skill (includes /retro global cross-project mode)
-├── bin/             # CLI utilities (gstack-repo-mode, gstack-slug, gstack-config, gstack-wtree, gstack-evidence, gstack-issue-guard, etc.)
+├── careful/         # /careful skill; bin/check-careful.sh (PreToolUse destructive-command hook) + bin/hook-extract.sh (shared hook helpers: payload extraction, deny JSON, gstack_hook_state_root)
+├── freeze/          # /freeze skill; bin/check-freeze.sh (PreToolUse edit-boundary hook; sources careful/bin/hook-extract.sh, fails closed)
+├── guard/, unfreeze/  # /guard (careful + freeze in one), /unfreeze
+├── gstack-upgrade/  # /gstack-upgrade skill + migrations/ (run after ./setup during an upgrade)
+├── bin/             # CLI utilities (gstack-repo-mode, gstack-slug, gstack-config, gstack-wtree, gstack-evidence, gstack-issue-guard, gstack-relink, etc.)
 ├── document-release/ # /document-release skill (post-ship doc updates + Diataxis coverage map)
 ├── document-generate/ # /document-generate skill (Diataxis doc generator: tutorial/how-to/reference/explanation)
 ├── cso/             # /cso skill (OWASP Top 10 + STRIDE security audit)
@@ -70,14 +75,14 @@ gstack/
 ├── extension/       # Chrome extension (side panel + activity feed + CSS inspector)
 ├── lib/             # Shared libraries (worktree.ts, egress-receipt.ts, context-bill.ts, redact-engine.ts, tracker-guard.ts, version-source.ts, code-intelligence/)
 ├── patches/         # bun `patchedDependencies` patches (playwright-core windowsHide)
-├── docs/designs/    # Design documents
+├── docs/designs/    # Design documents (incl. fork-port-residual-2026-09/ evaluation evidence)
 ├── setup-deploy/    # /setup-deploy skill (one-time deploy config)
 ├── .github/         # CI workflows + shared composite actions (.github/actions/) + Docker image (claude CLI pinned)
 │   ├── workflows/   # evals.yml (E2E on Ubicloud), quality-gate.yml (secret scan), dependency-review.yml, osv-scanner.yml, skill-docs.yml, actionlint.yml, and 8 more (windows, periodic evals, release gates, ci-image)
 │   └── docker/      # Dockerfile.ci (pre-baked toolchain + Playwright/Chromium)
 ├── contrib/         # Contributor-only tools (never installed for users)
 │   └── add-host/    # /gstack-contrib-add-host skill
-├── setup            # One-time setup: build binary + symlink skills
+├── setup            # One-time setup: build binary + best-effort Chromium bootstrap + link skills (ownership-gated)
 ├── SKILL.md         # Generated from SKILL.md.tmpl (don't edit directly)
 ├── SKILL.md.tmpl    # Template: edit this, run gen:skill-docs
 ├── ETHOS.md         # Builder philosophy (Boil the Ocean, Search Before Building)