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>

CLAUDE.md

@@ -186,10 +186,10 @@ failure modes. The sidebar spans 5 files across 2 codebases (extension + server)
 with non-obvious ordering dependencies. The doc exists to prevent the kind of
 silent failures that come from not understanding the cross-component flow.
 
-## Vendored symlink awareness
+## Dev symlink awareness
 
 When developing gstack, `.claude/skills/gstack` may be a symlink back to this
-working directory (gitignored). This means skill changes are **live immediately** —
+working directory (gitignored). This means skill changes are **live immediately**,
 great for rapid iteration, risky during big refactors where half-written skills
 could break other Claude Code sessions using gstack concurrently.
 
@@ -204,9 +204,11 @@ symlink or a real copy. If it's a symlink to your working directory, be aware th
 with a SKILL.md symlink inside (e.g., `qa/SKILL.md -> gstack/qa/SKILL.md`). This
 ensures Claude discovers them as top-level skills, not nested under `gstack/`.
 Names are either short (`qa`) or namespaced (`gstack-qa`), controlled by
-`skill_prefix` in `~/.gstack/config.yaml`. When vendoring into a project, run
-`./setup` after symlinking to create the per-skill directories. Pass `--no-prefix`
-or `--prefix` to skip the interactive prompt.
+`skill_prefix` in `~/.gstack/config.yaml`. Pass `--no-prefix` or `--prefix` to
+skip the interactive prompt.
+
+**Note:** Vendoring gstack into a project's repo is deprecated. Use global install
++ `./setup --team` instead. See README.md for team mode instructions.
 
 **For plan reviews:** When reviewing plans that modify skill templates or the
 gen-skill-docs pipeline, consider whether the changes should be tested in isolation