Fix stale @starknet-react/core import and cairo test arity mismatch

[tu11aa]

Summary

• app/page.tsx:8 imported useBlockNumber from @starknet-react/core, the old package name. The repo migrated to @starknet-start/react (declared as ^1.0.8 in package.json); every other hook usage already points there. Repointed the import — @starknet-start/react does export useBlockNumber, verified against the package's type declarations.
• contracts/tests/test_contract.cairo:110 called set_greeting(new_greeting, Option::Some(500)) with 2 args; the contract signature takes 3 (new_greeting, option_amount, option_token), causing a compile error (E2030) that failed the whole test suite before any test could run. Added the missing token arg (Option::Some(ETH_TOKEN_CONTRACT_ADDRESS), matching the sibling test_transfer_eth pattern at line 59) so the call now exercises the intended "insufficient allowance" panic path.

Diff is two lines of source changed (plus the corresponding cairo call reformatting) — no refactors, no unrelated cleanup. deployedContracts.ts untouched (D1, out of scope).

Proof (pasted command output)

Compile: ⏭️ Skipping compilation - all contracts are up to date (contracts/src unchanged by this PR)

Test:

Collected 5 test(s) from contracts package
Running 0 test(s) from src/
Running 5 test(s) from tests/
[PASS] contracts_integrationtest::test_contract::test_withdraw_not_owner
[PASS] contracts_integrationtest::test_contract::test_set_greetings
[PASS] contracts_integrationtest::test_contract::test_set_greeting_no_allowance
[PASS] contracts_integrationtest::test_contract::test_transfer_eth
[PASS] contracts_integrationtest::test_contract::test_transfer_strk
Tests: 5 passed, 0 failed, 0 ignored, 0 filtered out

Compile-clean (E2030 gone) and full pass, including the 3 #[fork("SEPOLIA_LATEST")] tests (network was reachable this run).

next:check-types: exit 0, clean (verified against a real deploy so the "Strk"|"Eth" narrowing from the empty deployedContracts.ts stub isn't masking anything)

yarn build: succeeded, all 8 routes generated

next dev (port 3002): curl -o /dev/null -w HTTP_STATUS http://127.0.0.1:3002/ → HTTP_STATUS:200

Test plan

• yarn compile
• yarn test (5/5 pass)
• yarn next:check-types (exit 0)
• cd packages/nextjs && yarn build
• next dev on port 3002, curl / → 200

[tu11aa]

Additional proof requested: `yarn format:check` / `scarb fmt --check` both pass clean (exit 0) on this branch — no reformatting needed.