Improved subject matching: detect subjects starting with the same text #344
Description
Enhancement: When creating a filter from multiple selected messages, quickFilters checks whether all selected message subjects start with the same sequence of words.
Subject normalization is applied first: blacklisted words are removed (issue 343) using the existing subject-cleanup logic in getMailKeyword(). The common-prefix detection therefore operates on cleaned subjects, not the raw subject lines.
If a common subject start is detected across all selected mails (for example Discord Payment Succeeded), the user is prompted:
“Found a common subject start: ‘Discord Payment Succeeded’ – shall we use this as the only subject search condition?”
If confirmed, the filter will use this shared subject prefix as a single Subject contains condition instead of multiple individual subject fragments.
This results in filters that are:
- more accurate
- easier to read
- less prone to false positives
Explicit subject prefixes such as [Project X] or {Invoicing} are treated as literals and are used directly without prompting.