Make email aliases case-insensitive

[Copilot]

Problem

Email addresses are case-insensitive according to RFC standards, but the email forwarding worker was treating aliases as case-sensitive. This meant that [email protected] would work, but [email protected] or [email protected] would be rejected, causing confusion for users.

Solution

This PR normalizes all alias and group comparisons to lowercase throughout the codebase, making email address matching case-insensitive while maintaining all existing functionality.

Changes Made

Core Logic Updates:

• Modified alias matching in Config.recipientConfig to convert both aliases and recipient accounts to lowercase before comparison
• Updated Config.aliases and Config.groups getters to return lowercase values
• Fixed group matching in Config.targetIsGroup to use lowercase comparison
• Updated delimited target matching in Config.targetFromRecipientWithDelimiter to use lowercase recipient account
• Enhanced Config.emailAddressesForGroup to perform case-insensitive group lookups
• Updated Processor._handleDelimitedTarget to use case-insensitive alias matching

Type Safety Improvements:

• Made groups and type fields optional in AccountsForConfigType interface to reflect actual usage patterns and prevent runtime errors

Testing

Added comprehensive test coverage for case-insensitive matching:

• Uppercase aliases ([email protected])
• Mixed case aliases ([email protected])
• Uppercase group aliases ([email protected])
• Uppercase aliases with suffixes ([email protected])
• Mixed case group aliases with suffixes ([email protected])

All 15 tests passing (10 existing + 5 new).

Impact

✅ No breaking changes - existing lowercase aliases continue to work exactly as before
✅ Improved user experience - uppercase and mixed-case variations now work correctly
✅ Aligns with standard email behavior per RFC specifications

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Address aliases are case sensitive</issue_title>
<issue_description>It's common for email addresses to be case insensitive, so let's support that and eliminate any issues that may arise from differently cased aliases.</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #30

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.