Add Nightly to Canton Wallet Directory

[NorbertBodziony]

Type of submission

• New wallet application

Summary

Adds Nightly to the Canton Foundation Wallet Directory with its wallet
overview and four documentation-backed Canton capability claims: Canton Coin
support, two-step CC transfers, transfer memo tags, and the CIP-0103 dApp API.

Checklist

• wallets/nightly.yaml added (self-attestation)
• A heading added to proofs/nightly/nightly-self-attestation.md for every feature claimed as supported: true
• python3 scripts/generate_table.py was run and the regenerated WALLET_DIRECTORY.md is included
• Confirmed membership in #ext-temp-party-scaling and set slack_party_scaling_channel_joined: true

Additional context

Nightly confirms that signup rate-limiting and circuit-breaker controls can be
demonstrated to maintainers on request.

This initial self-attestation uses Nightly's public product documentation and
open-source Canton integration as evidence. Transaction update IDs and
screenshots can be added in a follow-up.