core: implement protocol pause mechanism

[EmeditWeb]

Problem

There is no emergency pause mechanism. If a critical
bug is found or the protocol is under attack, there
is no way to halt operations.

What To Build

1. Add paused flag to parameters contract
2. Add pause() and unpause() functions
3. Add check_not_paused() to all contracts

Files To Touch

• contracts/parameters-contract/src/lib.rs
  All 5 contract lib.rs and errors.rs files

Acceptance Criteria

• pause() halts all protocol mutations
• unpause() restores normal operation
• View functions unaffected by pause
• Only admin can pause/unpause

Mandatory Checks Before PR

• cargo build passes
• All tests pass
• PR references this issue

[Iwayemi-Kehinde]

I would like to work on this issue as I have reviewed the scope, I should have a PR Ready in 50 minutes.

[mofejo1]

kindly assign this to me

[grantfox-oss]

🦊 GrantFox — @mofejo1 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #21)
2. Your PR will be reviewed by the StepFi-app maintainers

Good luck! Track your progress on GrantFox.