Fix unfinished setup/docs and platform metadata placeholders

[KuriGohan-Kamehameha]

Summary

• Fill the empty First-Time Setup Wizard section in README and fix setup list numbering/structure.
• Replace silent exception swallowing in platforms/generate_index.py with explicit handling and error visibility.
• Fill platform-level null descriptions across platform manifests with baseline descriptions.
• Add explicit no-scraper note to platform descriptions where scraperSourceList is empty (8 platforms).
• Normalize trailing newline in touched JSON files.

Build/Validation

• python3 -m py_compile platforms/generate_index.py platforms/curator.py
• python3 -m json.tool platforms/index.json
• python3 -c "import json; from pathlib import Path; [json.loads(p.read_text(encoding='utf-8')) for p in Path('platforms').glob('*.json')]; print('ok')"
• python3 platforms/generate_index.py (executed successfully; no errors in captured log)

Notes

• Left player-level description nulls untouched (31 remaining), since this change focuses on platform-level placeholders.
• Reverted accidental index churn so platforms/index.json stays unchanged in this PR.