Add Confidential Note Fungible Token Delivery extension

🧐 Motivation

Without on-chain delivery, a recipient can only learn about an incoming note through an out-of-band channel — unusable for a real wallet.

📝 Details

contracts/src/token/extensions/ConfidentialNoteFungibleTokenDelivery.compact

• Delivers each output note's (value, nonce) to the owner's encryption key encPk = g^encSk on chain, so recipients discover funds from chain data alone.
• Wallet flow: scan _deliveries, trial-decrypt with the account's encryption secret (the extension's exported recoverNote pure circuit, built on EcdhMask), keep the notes whose recomputed commitment exists in the core's tree.
• Imports no token module; the consumer calls _deliver next to its emission policy.

Landed in #679 (draft). Builds on crypto/EcdhMask with a Field plaintext pad (#735); the Note / Delivery structs and OZ:note:* tags live here, not in crypto/.