docs: align command docs with shipped behavior (#2169)

- multi-{plan,execute,backend,frontend,workflow}.md: add an in-file
  prerequisite note for the external ccg-workflow runtime. README.md already
  warns these commands need codeagent-wrapper and the .ccg prompt tree, but
  users meeting them via the installed slash commands never see the README;
  the commands-core module still installs all five by default
- quality-gate.md: describe what scripts/hooks/quality-gate.js actually does.
  The doc advertised '/quality-gate [path] [--fix] [--strict]' with lint/type
  checks, but the script reads the file path from hook stdin JSON, toggles
  behavior via ECC_QUALITY_GATE_FIX / ECC_QUALITY_GATE_STRICT env vars, and
  runs formatters only (Biome/Prettier, gofmt, ruff format)
- claude-devfleet SKILL.md: add a Setup section pointing at the DevFleet
  server repository (github.com/LEC-AI/claude-devfleet, already disclosed in
  mcp-configs/mcp-servers.json) plus the SECURITY.md port-verification note;
  the skill previously assumed a running instance with no way to obtain one
- regenerate docs/COMMAND-REGISTRY.json for the quality-gate description

skills/claude-devfleet/SKILL.md

@@ -10,11 +10,19 @@ origin: community
 
 Use this skill when you need to dispatch multiple Claude Code agents to work on coding tasks in parallel. Each agent runs in an isolated git worktree with full tooling.
 
-Requires a running Claude DevFleet instance connected via MCP:
+## Setup
+
+The DevFleet server is a separate project, not bundled with ECC. Install and
+run it from its repository first: <https://github.com/LEC-AI/claude-devfleet>
+
+Then connect the running instance via MCP:
 ```bash
 claude mcp add devfleet --transport http http://localhost:18801/mcp
 ```
 
+Before first use, verify the process listening on port 18801 is the DevFleet
+binary you installed (see SECURITY.md on localhost MCP servers).
+
 ## How It Works
 
 ```