fix(creators): paginate admin applications list and bound digit inputs

[mopxam-art]

Why

The admin applications review endpoint GET /v1/admin/creators/applications returned the entire collection with no pagination, causing performance degradation as application volume grew. Additionally, GET /v1/creators/applications/:id/create-project-tx accepted arbitrary-length digit strings for sequence and maturity_date without length or value bounds, causing large inputs (such as 400-digit numbers) to overflow Number(maturityRaw) to Infinity and trigger 500 crashes during XDR encoding.

What

• Added limit (default 20, max 100) and offset (default 0) pagination parameters to GET /v1/admin/creators/applications returning { applications, total, limit, offset, has_more }.
• Enforced digit length cap (<= 19 characters) on sequence, maturity_date, and whitelister_sequence to prevent overflow and reject invalid inputs with HTTP 400.
• Validated maturity_date against u64::MAX and Number.MAX_SAFE_INTEGER, returning structured 400 bad request errors instead of 500 runtime exceptions.
• Hardened buildCreateProjectTx and buildUnsigned in src/lib/creatorOnboarding.ts with explicit input validation throwing CreatorValidationError.
• Authored comprehensive test suite covering pagination slicing, boundaries, combinatorial parameters, and rejection controls (src/__tests__/creator-admin-pagination-and-bounds.test.ts).

Verified

• All 117 unit and integration tests pass cleanly (npx jest src/__tests__/creator-admin-pagination-and-bounds.test.ts).
• Existing creator onboarding test suite passes cleanly (npx jest src/__tests__/creator-onboarding.test.ts).
• TypeScript compiler clean (npx tsc --noEmit).
• Codebase linter clean (npm run lint).
• Production build succeeds (npm run build).

Closes #890