docs: added AGENTS.md files

[goncalopinto1]

Closes #1872

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 6%. Comparing base (ddbc118) to head (843610f).
⚠️ Report is 2 commits behind head on develop.

❌ Your project check has failed because the head coverage (6%) is below the target coverage (70%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

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##           develop   #1873   +/-   ##
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  Coverage        6%      6%           
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  Files           38      38           
  Lines         2143    2143           
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  Hits           125     125           
  Misses        2018    2018           

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[pedroafmonteiro]

The content of each AGENTS.md looks very good, but I think we should restructure how we give this information to the agents themselves.

First, I think we should have a root AGENTS.md referencing the AGENTS.md of each package inside uni (in our case, uni_app and uni_ui) and a quick summary of what the project is about.

Then, instead of inserting a new AGENTS.md file inside each feature folder, we should create a docs directory exclusively designed for agents, because I think the directories could start to get a little bloated for humans with files not made for them. With this, each AGENTS.md package file could reference those other files when needed. For example:

For our state management solution inside this app, we use Riverpod. Check out our guidelines when working with Riverpod at: ./docs/RIVERPOD.md

This is just an idea and opinion, let me know what you think! Also I purpose everyone at @NIAEFEUP/uni to give their opinion about these PR since it would affect everyone who uses an agent to assist with their work!