feat: add pagination to admin disputes, emergency withdraw endpoint, share price endpoint, and webhook retry processor tests

[aadviksinghdebug]

Implements 4 backend features/tests:

Closes #944 — Pagination for admin loan disputes

• Cursor-based pagination on GET /admin/loan-disputes (and JWT GET /admin/disputes)
• Default page size 50, max 100, newest-first ordering
• Returns next_cursor and has_next in page_info envelope

Closes #945 — Emergency withdraw endpoint

• buildEmergencyWithdrawTx in sorobanService (calls emergency_withdraw on LendingPool)
• POST /pool/build-emergency-withdraw with Zod validation, JWT ownership check, idempotency
• Reuses existing POST /pool/submit for signed XDR submission

Closes #946 — Share price endpoint

• GET /pool/:token/share-price returning the on-chain share price (scaled by 1e6) plus human-readable ratio
• 30-second Redis cache TTL to absorb burst requests

Closes #954 — Webhook retry processor tests

• 8 unit tests covering retry lifecycle, backoff scheduling, circuit-breaker (max attempts open/half-open/close), and subscriber isolation