feat: add milestone title and criteria fields to CreateVault

[Tboy123-emm]

Summary

Closes #291

Adds milestoneTitle and milestoneCriteria fields to the CreateVault form, addressing the gap where a vault's defining concept was never captured at creation time.

Changes

• src/utils/vaultValidation.ts: Extended CreateVaultFormValues type with milestoneTitle and milestoneCriteria. Added validation: non-empty (trims whitespace), max 100 chars for title, max 500 chars for criteria.
• src/pages/CreateVault.tsx: Added state and Field components for both new fields. Inline errors clear on change. Both fields included in the submit payload console.log.
• src/utils/__tests__/vaultValidation.test.ts: Updated all existing validateCreateVault calls to include new fields; added 8 new test cases (empty, whitespace-only, over-length, at-max-length for both fields).
• src/pages/__tests__/CreateVault.test.tsx: Added fillValidForm helper; updated all existing tests to fill new fields; added 5 new test cases for milestone field validation and payload.

Test Results

✓ src/pages/__tests__/CreateVault.test.tsx  (21 tests)
✓ src/utils/__tests__/vaultValidation.test.ts  (19 tests)

Test Files  2 passed (2)
      Tests  40 passed (40)

All 40 tests pass. Pre-existing failures in other test files (VaultTransactions window.matchMedia, ThemeContext jest is not defined) are unrelated and unchanged.

Coverage on Changed Lines

All new branches (empty, whitespace-only, over-length, at-exactly-max-length, valid) are explicitly tested.

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[GBOYEE]

@GBOYEE has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

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

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