feat(ci): ZK-065 full ZK validation pipeline and artifact drift detection

[s6pa1rta3n-lab]

Summary

Implements the comprehensive ZK validation pipeline and companion script specified in Issue #309 (ZK-065).

Changes

• .github/workflows/zk-full-validation.yml: Consolidated CI workflow with manifest validation, Nargo workspace check and tests, SDK ZK validation, deterministic artifact drift detection, and a consolidated branch protection gate.
• scripts/zk-full-validation-local.sh: Companion script mirroring all CI stages locally, supporting --all, --circuits, --sdk, --manifest, --drift, and --rebuild.
• circuits/lib/src/validation/fee.nr: Cleaned non-ASCII characters and removed invalid #[cfg(test)] attribute so Nargo compiles cleanly.
• circuits/withdraw/src/tests.nr: Removed duplicate #[test] decorator.

Acceptance Criteria Checklist

• Full ZK validation pipeline executes cleanly in CI from a fresh checkout.
• Manifest validation checks schema format, backend identity, circuit entries, and commitment vectors.
• Circuit checks verify workspace syntax and test coverage (nargo check, nargo test).
• SDK ZK validation executes proof smoke tests and core ZK test suites.
• Artifact determinism and drift detection validates bytecode against committed artifacts and manifest.
• Local script (scripts/zk-full-validation-local.sh) reproduces identical checks and exits cleanly.
• Scoped strictly to ZK validation without dependencies on frontend or contract deployment paths.

Closes #309

Payout Routing

• EVM (Base/Arbitrum/Polygon/ETH): 0xF46C9F6d70C50BF81ef3588AB523a90a594a2F89
• Stellar: GCL6OXAMLD75BMTINA6EMRUDWK5THQUSHMYNLSNBCJAPZJHNYJTUNIBC