docs: document permissionless functions in creditline-contract

[EmeditWeb]

Problem

mark_defaulted (lib.rs:486) and apply_late_fees (lib.rs:898) are permissionless — they do not call require_auth(). This may be intentional (anyone can trigger a default on overdue loans), but it is not documented anywhere.

What To Build

1. Add Rust doc comments to both functions explaining why they are permissionless
2. Document the security implications

Files To Touch

• contracts/creditline-contract/src/lib.rs — lines 486, 898

Acceptance Criteria

• Both functions have doc comments explaining permissionless design
• cargo doc passes

Mandatory Checks

• context/ files read
• cargo build passes
• PR references this issue

[AugistineCreates]

Hi, I'd like to work on this issue! because I am very conversant with solving problems like this, and i can submit the pr with 48hr