Align contributor onboarding Discord routing with standardized #development channel

## Summary
The contributor onboarding skill currently routes contributors who are blocked during local setup to the `#help` Discord channel, while the related AI policy and workflow documents standardize coordination on `#development`.

## Why this follow-up is needed
This mismatch can send contributors to the wrong channel and makes the onboarding flow inconsistent with the rest of the repository's documented workflow.

## Affected area
- `contributor-onboarding/SKILL.md`

## Requested change
Update the onboarding setup fallback so contributors are directed to the same Discord channel used elsewhere in the skill docs:
- Keep the existing build/run check flow
- Keep the `.agent/instructions/setup.md` context pointer
- Replace the `#help` referral with the standardized `#development` channel guidance

## Acceptance criteria
- The setup fallback in `contributor-onboarding/SKILL.md` no longer references `#help`
- The onboarding guidance uses `#development` consistently with the other skill documents
- The onboarding flow remains otherwise unchanged

## Backlinks
- Requested from PR review: https://github.com/AOSSIE-Org/Skills/pull/2
- Review comment: https://github.com/AOSSIE-Org/Skills/pull/2#discussion_r3544210703

Requested by: @kpj2006

Open contributor-onboarding/SKILL.md and locate the setup fallback that refers contributors to #help. Keep the existing build/run check flow and the .agent/instructions/setup.md context pointer, then update only the referral to use #development. Done means the file no longer references #help and the onboarding guidance matches the stated acceptance criteria.

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