feat: add mobile vault capability gate

[Myart352]

PR: Mobile Vault Capability Gate (#331)

Summary

Gate vault UI actions based on available SDK or contract capabilities. Each vault action (deposit, withdrawal, lock creation, and matured-lock withdrawal) is individually checked with clear user-facing explanations when unsupported.

Changes

New Files

• src/types/vault.ts — Added VaultActionCapability, VaultCapabilities, VaultAction types for per-action capability state (supported/unsupported/loading).
• src/utils/vaultCapabilities.ts — Centralized capability check utility: evaluateVaultCapabilities(), isActionSupported(), getActionUnsupportedReason(), getActionUnsupportedDetail().
• src/hooks/useVaultCapabilities.ts — Reactive hook that combines wallet, vault config, and feature flag states into a capabilities map.

Modified Files

• app/(tabs)/vault.tsx — Capability-gated deposit, withdraw, and lock buttons with disabled states and explanatory notices. Fixed broken handleConfirmAction logic.
• src/components/VaultLockList.tsx — Added unlockDisabledReason prop; shows disabled "Unlock Unavailable" button with styling when unlock is not supported.
• src/components/VaultConfirmModal.tsx — Added optional capabilityWarning prop shown in the modal detail section.
• src/hooks/index.ts — Exported useVaultCapabilities.
• docs/vault-sdk-capability-assumptions.md — Updated with capability gate architecture, action table, and future SDK integration path.

Acceptance Criteria

• Capability gate is added
• Unsupported actions are disabled or hidden
• User-facing explanation is shown
• SDK capability assumptions are documented
• Fallback UI is provided (VaultUnavailableState for full unavailability)

Testing

• Verified no TypeScript errors in modified files
• All pre-existing tests continue to pass
• Capability state updates reactively when wallet/vault state changes

Branch

feat/mobile-three-features

Issue

Closes #331