feat: team-friendly gstack install mode (v0.15.7.0) (#809)

* feat: add gstack-settings-hook for atomic Claude Code hook management

DRY helper for adding/removing SessionStart hooks in ~/.claude/settings.json.
Handles missing files, deduplication, malformed JSON, and atomic writes
(.tmp + rename) to prevent corruption on crash or disk-full.

Part of team-install-mode feature (credit: Jared Friedman).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add gstack-session-update for automatic team updates

SessionStart hook target that auto-updates gstack at session start.
Background fork (zero latency), throttled to once/hour, with lockfile
(mkdir + PID), stale lock recovery, GIT_TERMINAL_PROMPT=0, and debug
logging to ~/.gstack/analytics/session-update.log.

Part of team-install-mode feature (credit: Jared Friedman).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add --team, --no-team, -q flags to setup

--team enables auto_upgrade and registers SessionStart hook via
gstack-settings-hook. --no-team reverses it. -q/--quiet suppresses
all informational output (for hook-triggered setup runs). --local
now prints a deprecation warning.

Replaces ~20 echo calls with log() helper for quiet mode support.

Part of team-install-mode feature (credit: Jared Friedman).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add gstack-team-init for repo-level team bootstrapping

Two modes: 'optional' (gentle CLAUDE.md suggestion) and 'required'
(CLAUDE.md enforcement + .claude/hooks/check-gstack.sh PreToolUse hook
that blocks work without gstack installed). Atomic JSON writes,
idempotent, prints git add instructions.

Part of team-install-mode feature (credit: Jared Friedman).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: deprecate vendoring, document team mode, clean up uninstall

- README: replace "Step 2: Add to your repo" vendoring instructions
  with team mode (./setup --team + gstack-team-init)
- CLAUDE.md: rename "Vendored symlink awareness" to "Dev symlink
  awareness", add deprecation note
- CONTRIBUTING.md: remove vendoring language from prefix section
- bin/gstack-uninstall: clean up SessionStart hook on uninstall

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add vendoring deprecation detection to skill preamble

Detects vendored gstack in CWD (.claude/skills/gstack/ that's not a
symlink and has VERSION or .git). Outputs VENDORED_GSTACK: yes/no.
Adds generateVendoringDeprecation() section that offers one-time
migration to team mode via AskUserQuestion.

Part of team-install-mode feature (credit: Jared Friedman).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: regenerate SKILL.md files with vendoring deprecation preamble

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: team mode (v0.15.7.0) — credit Jared Friedman

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add integration tests for team mode (20 tests)

Covers gstack-settings-hook (add, remove, dedup, preserve existing,
atomic write), gstack-session-update (guards, throttle, non-fatal),
gstack-team-init (optional, required, enforcement hook, idempotent),
and setup flags (-q, --local deprecation).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## [0.15.13.0] - 2026-04-04 — Team Mode
+
+Teams can now keep every developer on the same gstack version automatically. No more vendoring 342 files into your repo. No more version drift across branches. No more "who upgraded gstack last?" Slack threads. One command, every developer is current.
+
+Hat tip to Jared Friedman for the design.
+
+### Added
+
+- **`./setup --team`.** Registers a `SessionStart` hook in `~/.claude/settings.json` that auto-updates gstack at the start of each Claude Code session. Runs in background (zero latency), throttled to once/hour, network-failure-safe, completely silent. `./setup --no-team` reverses it.
+- **`./setup -q` / `--quiet`.** Suppresses all informational output. Used by the session-update hook but also useful for CI and scripted installs.
+- **`gstack-team-init` command.** Generates repo-level bootstrap files in two flavors: `optional` (gentle CLAUDE.md suggestion, one-time offer per developer) or `required` (CLAUDE.md enforcement + PreToolUse hook that blocks work without gstack installed).
+- **`gstack-settings-hook` helper.** DRY utility for adding/removing hooks in Claude Code's `settings.json`. Atomic writes (.tmp + rename) prevent corruption.
+- **`gstack-session-update` script.** The SessionStart hook target. Background fork, PID-based lockfile with stale recovery, `GIT_TERMINAL_PROMPT=0` to prevent credential prompt hangs, debug log at `~/.gstack/analytics/session-update.log`.
+- **Vendoring deprecation in preamble.** Every skill now detects vendored gstack copies in the project and offers one-time migration to team mode. "Want me to do it for you?" beats "here are 4 manual steps."
+
+### Changed
+
+- **Vendoring is deprecated.** README no longer recommends copying gstack into your repo. Global install + `--team` is the way. `--local` flag still works but prints a deprecation warning.
+- **Uninstall cleans up hooks.** `gstack-uninstall` now removes the SessionStart hook from `~/.claude/settings.json`.
+
 ## [0.15.12.0] - 2026-04-06
 
 ### Fixed