Group gx help commands + quickstart and bump to 7.0.28

[NagyVikt]

Summary

Before:

```
COMMANDS
status Show GitGuardex CLI + service health ...
setup Install, repair, and verify guardrails ...
doctor Repair drift + verify ...
branch CLI-owned branch workflow surface ...
(… 16 more flat rows …)
```

A first-time user had to scan the whole 20-row list to figure out the intended "install → setup → first branch" sequence. This restructures the help surface into a grouped catalog with a Quickstart block that makes the bootstrap path visible up-front.

After (gx --help or gx with no args):

• QUICKSTART
  1. `gx setup`
  2. `gx branch start "" ""`
  3. `gx branch finish --via-pr --wait-for-merge --cleanup`
• COMMANDS (grouped)
  • Setup & health — Install, repair, and check a repo. Run these first on a new clone.
  • Branch workflow — The sandbox → commit → PR → merge loop for agent-owned branches.
  • Coordination — File locks, worktrees, hooks, and protected-branch policy.
  • Agents & reports — Review / cleanup bots, AI setup prompts, and safety reports.
  • Meta — Version + help.

Changes

• `src/context.js`: add `CLI_COMMAND_GROUPS` and `CLI_QUICKSTART_STEPS` as the grouped source of truth; derive `CLI_COMMAND_DESCRIPTIONS` from the groups so existing callers keep working.
• `src/output/index.js`: render the grouped catalog in both the plain (`NO_COLOR=1` / non-TTY) and colored tree-pipe layouts used by `usage()` and `printToolLogsSummary()`; add a QUICKSTART section to both surfaces.
• `package.json` / `package-lock.json`: bump `@imdeadpool/guardex` from `7.0.27` → `7.0.28` so the CLI UX change can publish on a fresh npm version.
• `README.md`: add a `### v7.0.28` release note (the metadata test requires a matching heading to exist for the current package version).

Test plan

• `node --test test/metadata.test.js test/output.test.js test/cli-args-dispatch.test.js` — 35 pass, 0 new failures.
• `NO_COLOR=1 node bin/multiagent-safety.js --help` — plain help renders the new QUICKSTART + grouped COMMANDS sections.
• `FORCE_COLOR=1 node bin/multiagent-safety.js` — no-args output renders the same groups inside the existing tree-pipe layout with colored group headers.
• Publish to npm (`npm publish`) once merged; `7.0.28` is still unpublished.

Known unrelated failures

• `critical runtime helper scripts and active-agents sources stay in sync with templates` / `setup provisions workflow files and repo config` — both are pre-existing on `main` (verified via `git stash` + rerun); caused by `vscode/guardex-active-agents/extension.js` drifting from its template. Not touched in this PR.

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