feat: add isolated billing mode for app deployments

[solimander]

Add isolated billing support (billTo: "app")

Adds SDK + CLI support for isolated billing, where an app is billed to its own address instead of the developer's. Maps to the new createAppWithIsolatedBilling contract function from eigenx-contracts#17.

Changes

• ABI: Add createAppWithIsolatedBilling, getBillingType, getAppsByBillingAccount
• SDK types: Add billTo?: "developer" | "app" to deploy option interfaces
• Contract caller: Conditional function name encoding in prepareDeployBatch(); new getBillingType() and getAppsByBillingAccount() read functions
• Deploy module: Reorder quota check after calculateAppID() so isolated billing can check quota against the app address; thread billTo through all three deploy paths
• App module: Expose getBillingType and getAppsByBillingAccount on AppModule
• CLI: Add --bill-to flag (developer | app, default developer)
• Exports: Add new functions to client/index.ts and browser.ts

Usage

ecloud compute app deploy --bill-to app

await compute.app.prepareDeploy({ ..., billTo: "app" });

Default behavior (billTo: "developer") is unchanged.