feat: typed vaultService data layer over mocks with integration-seam …

[jabir-dev788]

Closes #216

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Summary

Introduces a single vaultService data layer and shared Vault/
Milestone/VaultTransaction types, replacing four independent inline
mock arrays in Dashboard, Vaults, VaultDetail, and VaultTransactions.

Notable finding

The existing mocks didn't just have duplicated types — they disagreed on
actual values for the same vault id across files (e.g. "Gamma Fund" was
$4,200/active in Dashboard.tsx but $8,800/failed in Vaults.tsx and
VaultDetail.tsx). This PR treats VaultDetail.tsx's dataset as canonical
and unifies on it, which incidentally fixes that inconsistency. Documented
in docs/VAULT_DATA_LAYER.md.

Design note

VaultTransactions.tsx's transaction explorer uses a richer per-transaction
shape (fee, block, from/to, memo, status) that has no equivalent in other
pages' data. Rather than force those fields into the shared VaultTransaction
type (which would mean inventing data), it gets its own
VaultActivityRecord type and listAllActivity() method.

Changes

• src/types/vault.ts — canonical Vault/Milestone/VaultTransaction types
• src/services/vaultService.ts — async, mock-backed: listVaults,
  getVault, getTransactions, listAllActivity
• 4 pages refactored to consume the service instead of inline mocks
• docs/VAULT_DATA_LAYER.md — documents the contract-integration seam

Tests

vaultService.test.ts covers unknown vault id, empty transaction list,
and Promise-based resolution shape for all 4 methods.

No UI regressions

Each page renders the same structure; only the data source changed from
synchronous inline arrays to an async service call with a brief loading state.

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[GBOYEE]

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Implement following existing patterns and conventions. Add tests, ensure CI passes, and document any new API surface.

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