test(verifier): add typescript-solidity differential fuzz harness

[ericbsantana]

Description

• Add TS-Solidity differential fuzz harness under packages/protokoll/test/differential/ using vitest + Anvil + viem
• 5 mutation categories (gamma, c, s, roundId, publicKey) x 50 mutations per run, all rejected by verifyProof
• Extend the existing vitest CI job with foundry toolchain + forge build; total job time stays under 5 min

Checklist

• Code compiles (pnpm build and forge build both pass)
• All tests pass (pnpm test and forge test)
• Added tests that fail without the change (where applicable; required for bug fixes)
• Updated docs in packages/docs/ if user-facing behavior changed
• For contract changes: storage layout, gas, and redeploy implications noted in the description