feat: subcategory feature

[lucaantonelli]

🎯 Description

Working implementation of subcategory feature!

Closes: #198

📱 Changes

• Subcategories are shown as a list on each category page (following figma)
• Subcategories creation/editing page (only allow to choose name and icon, not color, since is the same of the parent category)
• Subcategories can be selected in transactions. Click on a category with subcategories, and it will shows with an animated list the subcategory, if you don't choose a subcategory, the parent is automatically selected
• Subcategories doesn't appear in the main category list, but only inside the parent editing page

🧪 Testing Instructions

Test the pages mentioned in the changes.

🔍 Checklist for reviewers

• Code is formatted correctly
• Tests are passing
• [] New tests are added (if needed)
• Style matches the figma/designer requests
• Tested on:
  • iOS
  • Android

[theperu]

@lucaantonelli I noticed a few things while testing:

• If I try to create multiple subcategories the page for creating them is already prefilled with the values from the previous one. (https://github.com/user-attachments/assets/33d5ce35-ba5b-407b-a2be-6deed3614923)
• In the transactions page I get an error after adding a transaction with a subcategory

• If I add a recurring transaction with a subcategory then it doesn't show in the planning page (https://github.com/user-attachments/assets/25b4aa48-a138-4a1b-a400-c2a21fdf9960)

[theperu]

@lucaantonelli I can see that all issues are fixed but there is still something I would like to change. Now the subcategories are treated as a normal category in the transactions page and they are just pushed at the bottom which looks a bit odd to me (Video 🎥)

Screen.Recording.2026-01-19.at.20.03.07.mov

I would suggest to group them inside their main category kinda like what I did here

Screen.Recording.2026-01-19.at.20.16.59.mp4

NOTE: I won't push this code because it's vibecoded and I don't trust it 😅

[federicopozzato]

I like it! I think it's good

[theperu]

LGTM! ✅