feat: add bridged assets (SEND, cbBTC, USDC.B, FRXUSD.B) to the asset registry

[crisog]

The Send bridge issues four token-standard instruments that aren't listed in the asset registry yet, so wallets can't resolve their metadata or show them. This adds those instruments — three on TestNet and four on MainNet.

TestNet — admin cantonwallet-send-bridge-registrar::1220f6ac…fe57:

symbol	instrument id
SEND	SEND
cbBTC.B	CBBTC.B
USDC.B	USDC.B

MainNet — admin cantonwallet-asset-relayer-instrument-operator::12202e6d…b71c:

symbol	instrument id
SEND	SEND.B
cbBTC.B	CBBTC.B
USDC.B	USDC.B
FRXUSD.B	FRXUSD.B

The instrument ids match each registrar's live registry, which is public and unauthenticated, so it can be confirmed directly:

# TestNet → SEND, USDC.B, CBBTC.B
curl -s "https://api.utilities.digitalasset-staging.com/api/token-standard/v0/registrars/cantonwallet-send-bridge-registrar::1220f6ac73835e1086f0d23aa42767e26234d175b4f8188399446c344bbfcdfbfe57/registry/metadata/v1/instruments"

# MainNet → SEND.B, USDC.B, FRXUSD.B, CBBTC.B
curl -s "https://api.utilities.digitalasset.com/api/token-standard/v0/registrars/cantonwallet-asset-relayer-instrument-operator::12202e6dd1f885994b22ca64e10582328bcd1a31b4fe69bf529982d31d57c8cab71c/registry/metadata/v1/instruments"

No existing entries are changed, and no DevNet entries are added.