fix(crypto): correct DeviceEntry publicKey validator length

[FSM1]

Summary

• Fixed DeviceEntry.publicKey validator checking for 130 hex chars (uncompressed secp256k1) instead of 64 hex chars (Ed25519 32-byte key)
• Updated test fixture to use correct 64-char Ed25519 key format
• Corrected docs/METADATA_SCHEMAS.md to document 64 hex chars

Context

Device keypairs are Ed25519 (generateDeviceKeypair() → 32-byte public key → 64 hex chars), but the validator in schema.ts was checking for 130 chars (copy-pasted from secp256k1 uncompressed key validation). This would reject real device keys on encrypt→decrypt round-trip. Found by CodeRabbit on PR #175.

Test plan

• All 225 crypto package tests pass (pnpm --filter @cipherbox/crypto test)
• Verified Rust desktop has no equivalent bug (uses serde, no manual length check)

🤖 Generated with Claude Code

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/device-registry-publickey-validator

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