feat(frontend): add Soroban contract invocation hook

[CMI-James]

Description

Add a reusable Soroban contract invocation hook for frontend contract calls.

Closes #144

Changes proposed

What were you told to do?

I was tasked with creating a useSorobanContract(contractId) React hook that abstracts direct Soroban smart-contract invocations for deployed contracts (bulk_payment, vesting_escrow, revenue_split).

Requirements included:

• Return invoke, loading, error, and result state
• Run simulateTransaction before every live submission
• Delegate wallet signing to useWalletSigning
• Decode on-chain results and return typed data
• Surface failures via useNotification toast errors

What did I do?

Added a dedicated Soroban invocation hook

Updated frontend/src/hooks/useSorobanContract.ts with:

• useSorobanContract(contractId) returning invoke, loading, error, and result
• Generic typed result support via a parseResult callback
• Contract-method invocation API that accepts method name + args

Integrated pre-flight simulation into invoke flow

Implemented invocation pipeline to:

• Build contract-call transaction XDR with Contract + TransactionBuilder
• Simulate the XDR using existing simulateTransaction(...)
• Block submission and raise error when simulation fails

Wired wallet signing through existing wallet hook

Integrated useWalletSigning by:

• Preparing transaction with Soroban RPC
• Signing prepared XDR through sign(...)
• Rebuilding signed transaction and submitting to Soroban RPC

Added on-chain result decoding and typed return

After submission and confirmation polling:

• Read return value from successful transaction
• Decode ScVal via scValToNative
• Return parsed typed value and tx hash in hook result state

Added robust error surfacing

Hook now:

• Tracks and exposes error state
• Emits user-facing toast failures through notifyError(...)
• Validates disconnected-wallet state before invocation

Check List (Check all the applicable boxes)

• My code follows the code style of this project.
• This PR does not contain plagiarized content.
• The title and description of the PR is clear and explains the approach.
• My commit messages styles matches our requested structure.
• My code additions will fail neither code linting checks nor unit test.
• I am only making changes to files I was requested to.

Screenshots / Testing Evidence

• Ran pnpm lint in frontend/ and no blocking lint errors were reported for this hook (only existing unrelated warning-level checks elsewhere)
• Ran pnpm build in frontend/ successfully
• Hook implementation was validated by code inspection against acceptance requirements