Encrypted memory search

[nikiwastaken]

Description

Encrypted in-memory message search and an opt-in indexedDB local message search

Based on #871 and #881

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).

I did not use AI for my changes. The original PRs were fully generated, but this PR will not exit draft until I've looked at all the code thoroughly and confirmed it's sane.