Replace panic!/panic_with_error! with typed errors; add missing error…

[happyboy24]

… tests

• Convert init() from panic_with_error!(AlreadyInitialized) to return Err(Error::AlreadyInitialized); change signature to Result<(), Error> so callers get a typed error not a trap
• Replace accept_admin ok_or(NotInitialized) with the new NoPendingAdmin variant for accurate error semantics
• Add NoPendingAdmin = 8 to the Error enum
• Doc-comment every Error variant for ABI documentation
• Remove now-unused panic_with_error import
• Convert init_is_one_shot test from #[should_panic] to try_init + assert_eq!(Err(Ok(Error::AlreadyInitialized)))
• Add 9 new tests covering NotInitialized on all admin entry- points and NoPendingAdmin on accept_admin

All 26 tests pass; grep confirms zero panic!/unwrap()/expect() in contract source.

Summary

Checklist

• Security: No private keys or sensitive data exposed. ZK circuit logic remains sound.
• Tests: New/modified logic is covered by tests (npm test passes).
• Scope: Changes are within the scope of the issue/feature.
• Documentation: Updated README or other docs if necessary.
  closes Audit: review all panic! sites in the validator contract and replace with proper errors #59