Add comprehensive documentation for impounded addresses feature

[Copilot]

This PR adds user-facing documentation for the impounded addresses feature that was implemented in docassemble-AssemblyLine PR #760.

While the API documentation was automatically generated and already included the new parameters and attributes, there was no user-facing documentation explaining what impounded addresses are, when to use them, or how to implement them in interviews.

What's Added

The new documentation section in /docs/style_guide/question_library/addresses.md includes:

Introduction: Clear explanation that impounded addresses are addresses that should be hidden or redacted on certain documents for safety or privacy reasons, commonly needed in domestic violence cases, restraining orders, or other sensitive legal situations.

When to use: Specific guidance on appropriate use cases:

• User's address needs to be kept confidential for safety reasons
• Court rules allow or require address impounding in your jurisdiction
• User may need some documents to show their full address (like for service), while other documents should redact it
• Need to collect the address for court records but hide it from opposing parties

Implementation examples: Both Assembly Line and vanilla Docassemble approaches for:

• Basic address collection with ask_if_impounded=True
• Phone number impounding with examples
• Display control using show_impounded=True parameter

Complete reference: List of all address display methods that support the show_impounded parameter, custom template guidance, and a working complete example.

Important warnings: About normalized_address() not respecting impounded status.

The approach was surgical and focused - adding one comprehensive section to existing documentation rather than creating new files or making extensive changes.

Fixes #436.

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