feat(frontend): add preflight simulation before value-moving transactions

[woahwhattheheck]

Summary

Closes #264.

Adds a read-only preflight simulation step for deposits and withdrawals so deterministic failures are caught before the wallet asks for a signature. Successful simulation is advisory only; contract-side validation and the provider result remain authoritative.

Trust boundary

• Preflight is a read-only check against the current wallet, connected network, and exact serialized transaction payload.
• status: ok never means the transfer is confirmed or settled.
• Sign + submit still run after a passing preflight; on-chain / provider outcome is final.
• Preflight never bypasses vault service validation.

Race / invalidation handling

• Each result is bound to fingerprint = network::serializedTx.
• Changing amount, wallet, or network marks the result stale and blocks signing until preflight is run again.
• Concurrent runs use a generation counter so outdated responses cannot overwrite newer state.

User-visible states

State	Behavior
running	“Running preflight…” — submit disabled
ok	Advisory pass message — signature may be requested
rejected	Actionable reason (stale balance, paused vault, contract rejection, network mismatch) — no signature
timeout / unsupported	Safe Retry preflight path — no signature
stale	Intent drifted — retry required before signing

Acceptance criteria

• Deposits and withdrawals do not request a signature when preflight detects a deterministic failure
• Preflight results are tied to the exact serialized transaction and connected network
• Provider timeouts and unsupported simulation responses produce a safe retry path

Test evidence

• test/utils/preflight.test.js — serialize / fingerprint / binding / signature gate
• test/services/preflight.test.js — success, contract rejection, timeout, unsupported, stale balance, paused vault, network mismatch, insufficient position
• test/hooks/usePreflight.test.jsx — changed payload, network switch, timeout retry
• test/components/DepositForm.preflight.test.jsx — no signAndSubmit on reject / timeout / stale / wrong network; success still signs

npm test — 236 passed. tsc -b — clean for touched packages.

Out of scope

• Replacing authoritative contract validation
• Redesigning wallet integrations