feat(account-abstraction): implement AccountContract SDK package

[Agbasimere]

Summary

Implements the @ancore/account-abstraction SDK package with an AccountContract class that wraps Soroban contract invocations for the Ancore account contract (contracts/account).

Changes

• AccountContract (src/account-contract.ts): TypeScript API for contract methods
  • initialize(owner) — invoke contract initialize
  • execute(to, function, args) — invoke contract execute
  • addSessionKey(publicKey, permissions, expiresAt) — invoke add_session_key
  • revokeSessionKey(publicKey) — invoke revoke_session_key
  • getSessionKey(publicKey) / getSessionKeyInvocation(publicKey) — get_session_key
  • getOwner() / getOwnerInvocation() — get_owner
  • getNonce() / getNonceInvocation() — get_nonce
  • call(method, ...args) and buildInvokeOperation(invocation) for building Stellar operations
• XDR helpers (src/xdr-utils.ts): Encode/decode for addresses, BytesN<32>, u64, permissions, symbols, and SessionKey structs
• Errors (src/errors.ts): Typed errors (AlreadyInitializedError, NotInitializedError, UnauthorizedError, etc.) and mapContractError() for contract/host errors
• Unit tests (src/__tests__/account-contract.test.ts): 24 tests with mocked server for AccountContract, XDR helpers, and error mapping
• Build/config: tsconfig.json for account-abstraction; tsconfig.json + build script update for @ancore/types (DTS resolution); jest.config.cjs and test deps; root package.json esbuild override; ui-kit vitest run so pre-push hook completes

Dependencies

• @stellar/stellar-sdk, @ancore/types, @ancore/stellar, @ancore/crypto

Testing

• pnpm test in packages/account-abstraction — all 24 tests pass
• Build: pnpm run build --filter=@ancore/types --filter=@ancore/account-abstraction

Closes #31 (if your issue number is different, replace it).

[Agbasimere]

@wheval pls merge.