Empty/stub pages are publicly reachable

[gjong]

Labels: content, bug, priority:P1
Parent issue: Epic: Documentation site overhaul

Problem
The following pages are empty or draft-only but may still be reachable/linked:

• content/how-to/advanced/rules.md (empty)
• content/how-to/advanced/scheduling.md (empty)
• content/how-to/your-finances/overview.md (empty)
• content/how-to/your-finances/contracts.md (draft: true, empty)
• content/getting-started/advanced/schedule-bills.md (draft: true, empty)
• content/getting-started/first-steps/_index.md (missing title in front matter)

Suggested fix

• For each: either write real content, set draft: true consistently, or add an explicit "Coming soon" placeholder.
• Uncomment/remove the corresponding sidebar entries in data/how-to.yaml (Transactions, Contracts) to match actual page state.
• Add the missing title front matter to first-steps/_index.md.

Acceptance criteria

• No page in production is both empty and linked from navigation.
• Sidebar entries in data/how-to.yaml match actual published content.
• first-steps/_index.md has a title.