fix: validate withdrawal address in watcher (#13)

[odiseusme]

Fixes #13.

Changes

• Adds ergo-lib-wasm-browser (^0.24.1) to apps/watcher dependencies
• Adds webpack/WASM configuration to apps/watcher/next.config.js (mirrors the experiments block from apps/rosen/next.config.js, plus output.webassemblyModuleFilename needed for output: 'export')
• Adds apps/watcher/src/utils/validateErgoAddress.ts — a browser-side Ergo address validator that lazy-loads the WASM module on first use
• Refactors the address field in apps/watcher/src/app/actions/@form/withdraw/page.tsx from register('address', { required }) to useController with an async validate rule, mirroring the pattern in apps/rosen/src/hooks/useBridgeForm.ts

Validation behavior

The validator uses Address.from_base58() from ergo-lib-wasm-browser, which accepts both mainnet and testnet Ergo addresses. The issue specifies "an Ergo address" (not "a mainnet Ergo address"), and a Watcher operator may be running a testnet deployment — restricting to mainnet would break testnet operators.

Error messages mirror the Rosen app's useBridgeForm exactly:

• Empty input: "Address cannot be empty" (intentional change from the previous "Address is required" to match Rosen)
• Invalid address: "Invalid Address"
• Unexpected error during validation: "Something went wrong! please try again"

Verification

• npm run build for apps/watcher succeeds; the .wasm chunk is emitted to out/_next/static/wasm/
• The WASM file is served with Content-Type: application/wasm and HTTP 200 from a static-server smoke test
• No new TypeScript errors introduced (verified by comparing npm run type-check output against the pre-PR baseline)

Notes for reviewers

• This PR is independent of Remove ignoreBuildErrors from Next config #8 and can land in either order. Both PRs touch apps/watcher/next.config.js but in non-overlapping ways.
• CI may show pre-existing type-check failures in apps/watcher/src/app/App.tsx until Remove ignoreBuildErrors from Next config #8 merges — those errors exist on the current dev branch and are exactly what Remove ignoreBuildErrors from Next config #8 fixes. They are not introduced by this PR.
• WASM bundle adds ~2.5 MB; lazy-loaded on first address validation, kept out of the initial page bundle.

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[odiseusme]

Verification of acceptance conditions (done locally via source inspection):

1. Error display: Uses react-hook-form's formState.errors.address.message rendered through the shared TextField's helperText prop (same @rosen-bridge/ui-kit component as Rosen). Visual parity follows from the shared component.

2. Validation logic: Equivalent to Rosen's by construction. Rosen's chain runs server-side: useBridgeForm → Server Action → @rosen-network/base.validateAddress → @rosen-bridge/address-codec → for ERGO_CHAIN: ergoLib.Address.from_base58(address). Our PR runs Address.from_base58(address) directly in the browser via ergo-lib-wasm-browser. Same Rust source, same accept/reject behavior. The Watcher's output: 'export' precludes Server Actions, which is why we go direct-to-WASM.

3. react-hook-form API: useController with async validate rule, mirroring apps/rosen/src/hooks/useBridgeForm.ts. Empty check ("Address cannot be empty"), validation call, fallback ("Invalid Address"), catch-all ("Something went wrong! please try again") — all identical strings to Rosen's flow.

One small UX delta: we trim whitespace on the input's onBlur before validation. Rosen's ErgoNetwork.toSafeAddress is a no-op pass-through (return address), so where Rosen would reject " 9fuoH... ", our form accepts it. We've kept this small UX improvement intentionally — happy to discuss if there's a reason to revert.