consolidate data key metadata and storage schema documentation

[grantfox-oss]

storage.rs contains key layout comments, but storage metadata is scattered across multiple modules. Consolidate and link storage layout docs to tests.
- Impacted files: app/contract/contracts/Folder/src/storage.rs, app/contract/contracts/Folder/src/types.rs, app/contract/contracts/Folder/src/storage_test.rs, app/contract/README.md, app/contract/docs/UPGRADE_SAFETY_GATE_IMPLEMENTATION.md, app/contract/docs/UPGRADE_SAFETY_GATE_QUICK_REFERENCE.md

[OluRemiFour]

I've checked the requirements and am confident I can resolve this efficiently. Happy to take it on.

[Tobi-8]

Can i be assigned to this
I have the knowledge and experience to handle this issue

[Tobi-8]

Can i be assigned to this
I have the knowledge and experience to handle this issue

[egwujiohaifesinachiperpetual-max]

Hello boss, Please assign this issue to me. i checked it out and im confident i will solve it
my eta is 4 hours

[blessedcodey-boy]

Hey Maintainer !!!!
I just went gone through the details of the issue and i will be capable of resolving it, I would love to be assigned to work on it. Thanks

[Promise278]

i have expereinced with system design and archceture i would love to work on these please

[grantfox-oss]

🦊 GrantFox — @farouqyakubu6-creator has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #335)
2. Your PR will be reviewed by the BlockDash-Studios maintainers

Good luck! Track your progress on GrantFox.