Learn the instrument from the registry and move to the vesting factory

[lmcorbalan]

User story / Problem statement

Currently the dApp builds a Splice transfer context from wallet-service and looks for an AmuletVestingFactory. It knows nothing about the token-forge instrument, and nothing on the ledger can tell it: the factory is this repo's own operator, but the instrument admin is a third party.

Expected outcome

The deployment the dApp loads carries the (admin, instrumentId) pair the registry reports, and points at the VestingFactory bootstrap now creates.

Acceptance criteria

• src/backend/registry.ts exposes fetchInstrument and fetchInstrumentConfig
• Deployment carries admin and instrumentId
• config.ts finds the factory at #vesting:Vesting:VestingFactory
• bootstrap creates a VestingFactory and no AmuletVestingFactory
• VITE_REGISTRY_URL is validated and defaults to http://localhost:3013
• A registry failure names the route it came from

Technical notes

/registry/metadata/v1/info reports only adminId; the instrument list is its own route. Zero or several instruments is a hard error, since this dApp knows exactly one. VITE_WALLET_RPC_URL is added beside, not renamed: transferContext.ts still reads it until task 3.