Sc reg 032 ipfs cid validations

[sweetesty]

Closes #386

---

This PR implements Enforce Job Description IPFS CID String Format Validations inside contracts/job_registry/src/lib.rs as specified in SC-REG-032.

What was done:

• CID format validation: Added a dedicated validator that checks all incoming job description strings against the IPFS CID format (CIDv0 Qm... base58 and CIDv1 bafy... base32) before any on-chain write; invalid formats are rejected with a typed InvalidCID error code
• Storage design: Heavy text fields (job descriptions, briefs) are stored exclusively as validated IPFS CIDs using Soroban persistent storage, keeping the WASM footprint within standard block boundaries
• Job ID → bid structure mappings: Maintained the clean DataKey::Bids(job_id) → Map<Address, Bytes> storage layout from the previous step, mapping freelancer addresses to their IPFS proposal hashes
• Ownership validation: Strict checks ensure only the original job creator can accept proposals; unauthorized calls return a dedicated typed error code
• State machine: Registry transitions cleanly through Open → Bidding → Assigned on bid acceptance; invalid transitions are rejected with specific error variants
• Checked math: All arithmetic on collateral amounts uses Rust checked operations (checked_add, checked_sub) to prevent overflow/underflow
• Inline annotations: All validation logic, storage keys, and entry points carry self-documenting comments per the project's architectural guidelines
• Unit tests: Comprehensive cargo test suite covering valid CIDv0/CIDv1 inputs, malformed CID rejections, ownership violations, late bids, and full state transition flows

Acceptance criteria met:

• ✅ Contract compiles and fits within Soroban WASM size limits
• ✅ State transitions cleanly to Assigned on successful bid acceptance
• ✅ Invalid CIDs, out-of-bounds inputs, and late submissions are blocked and return specific error codes

[vercel]

@sweetesty is attempting to deploy a commit to the mAzI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[drips-wave]

@sweetesty Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[soomtochukwu]

If you could just fix the merge conflicts ASAP