fix: --llms scoped to group doubles namespace in command names

[eduwass]

Problem

When using --llms (or --llms-full) scoped to a command group, the group segment is duplicated in command names:

$ my-cli auth --llms

Expected:

| `my-cli auth login` | Log in |
| `my-cli auth logout` | Log out |

Actual:

| `my-cli auth auth login` | Log in |
| `my-cli auth auth logout` | Log out |

This affects all output formats (md, json, yaml) for both --llms and --llms-full.

With nested groups the duplication compounds — e.g. app project deploy project deploy create instead of app project deploy create.

Cause

In Cli.ts, the scoping loop (lines 572–588) narrows scopedCommands to the sub-group and accumulates consumed tokens into prefix. The prefix is then correctly used to build scopedName (e.g. "my-cli auth"), but it's also passed to the collect helper functions (collectSkillCommands, buildManifest, buildIndexManifest), which prepend it again to each command name.

Fix

Pass an empty [] prefix to the collect helpers when scoped, since scopedName already carries the group path for display purposes. One-line change plus test updates.

Reproduction

import { Cli } from 'incur'

const cli = Cli.create('test')
const auth = Cli.create('auth', { description: 'Authentication' })
auth.command('login', { description: 'Log in', run: () => ({}) })
auth.command('logout', { description: 'Log out', run: () => ({}) })
cli.command(auth)

// Root: correct
await cli.serve(['--llms'])
// → `test auth login`, `test auth logout` ✅

// Scoped: before fix → `test auth auth login` ❌
// Scoped: after fix  → `test auth login` ✅
await cli.serve(['auth', '--llms'])

Test changes

All 815 tests pass. Updated 6 inline snapshots and 2 assertions in Cli.test.ts and e2e.test.ts that were asserting the buggy doubled-namespace behavior.