feat: show unread counts

[mavonx]

What?

Shows unread email counts next to folder names in the sidebar.

Why?

Folder list showed folder names only, making it impossible to see which folders have unread mail without opening each one.
This improves navigation efficiency.

Closes #645

[floatpanebot]

Hi @mavonx! Please fix the following issues with your PR:

• Title: Is too long (45 characters). The PR title must be strictly under 40 characters.

Formatting issues have been resolved. Thank you!

[mavonx]

@andrinoff

I've implemented the unread counters feature for the IMAP backend for now.

I also wanted to note that when folder names are initially loaded from the cache, there will be a delay before the counters display correctly once the server fetch completes. To remove this delay, I thought about storing the unread counter alongside each folder in folder_cache.json, but this introduces a consistency problem — when a user reads an unread email, I update the counter in memory (already done), but I'd also need to write the updated counter back to the cache on every read action.

Let me know if you have a different approach to handle this.

[andrinoff]

i'd cache this and load it from folder_cache @mavonx, it doesn't have to be a re-fetch every time you open matcha. as far as implementation goes, just add it to handler of reading an email (e.g. it is marked read, no matter what the server receives, it is handled, when an email is opened) just subtract 1 from the correct folder, and leave it to re-fetch to make sure it is correct later.

[mavonx]

@andrinoff

I already decrease the unread count from the selected folder in memory.

But just to make sure: if I load the counters from the cache and don't update the cached counters after each unread email is marked as read, then the counters will only stay correct while the user is in the same process/session, but if the user closes the current session and opens it again, they will see the outdated counter from the cache until the server fetch corrects it.

So, is that okay?

[andrinoff]

you should update the cache when an email is read (opened). when matcha is re-fetching it should also update the counter

[mavonx]

@andrinoff I'll check the tests tomorrow.