v1.16.0 — Grok Build support

Added

• Grok Build support: native .grok-plugin/ marketplace + plugin manifests so
  users can install with grok plugin marketplace add berkayturk/appstore-precheck and
  grok plugin install appstore-precheck --trust (or a direct path/GitHub install). The same
  SKILL.md and upload-guard hook work; Grok sets GROK_PLUGIN_ROOT and the CLAUDE_PLUGIN_ROOT
  alias used by hooks/hooks.json. The marketplace entry uses a URL source (Grok rejects a
  self-referential local source), so that flow installs GitHub main; install a path directly to
  test a local clone.
• install.sh grok: vendors the skill into .grok/skills/ (project or user scope). The
  default all target now also populates .grok/skills/ alongside .claude/skills/ and
  .agents/skills/.
• Docs, badge, AGENTS.md, version lockstep (check-versions), and install tests updated for the
  fifth host.

Fixed

• Upload guard no longer fails open on Grok Build (or Cursor): hooks/fastlane-guard.sh read
  only Claude Code's snake_case .tool_input.command, while Grok sends the same event camelCased
  as .toolInput.command and Cursor's shell event carries .command at the top level. The command
  came back empty and every fastlane deliver/pilot/release was allowed. Every plugin manifest
  wires this hook, so the guard now reads all three envelopes, and tests/test-guard.sh covers
  each.
• Block reason reaches the model on every host: the guard now also writes the deny as stdout
  JSON (decision: "deny" plus Claude Code's hookSpecificOutput.permissionDecision) alongside
  the stderr message. Grok honours a stdout deny for PreToolUse and documents stderr feedback
  only for Stop/SubagentStop, so Pierre's reason could previously be dropped there. Exit 2 is
  still the authority.