feat(adapter-midnight): Auto-generate Private State ID from contract and wallet address

[yug49]

Problem
When loading a Midnight contract, users were required to manually input a "Private State ID" field. This created unnecessary friction.

Solution
Auto-generate the privateStateId deterministically from contractAddress + walletAddress at transaction execution time.

// Deterministic ID generation
const privateStateId = generatePrivateStateId(contractAddress, walletAddress);
// Output: "midnight_<first12chars_of_sha256_hash>"

Changes

• Removed privateStateId form field from getContractDefinitionInputs()
• Made privateStateId optional in MidnightContractArtifacts interface
• Added generatePrivateStateId() utility using SHA-256 hash
• Auto-generate ID in EOA execution strategy when wallet is connected
• Updated all artifact validation paths (ZIP upload, URL loading, trimmed ZIP)
• Removed privateStateId from exported app artifacts (generated at runtime)

Testing

• Added unit tests for generatePrivateStateId() utility
• Updated existing tests to reflect optional privateStateId
• All 459 tests pass

Closes #263