Add pool share price endpoint

[Lucas-FManager]

Summary

Refs #946.

This adds a lender-only GET /api/pool/:token/share-price endpoint that reads the LendingPool get_share_price(token) value, returns the raw 1e6-scaled share price, a human-readable ratio, aggregate utilization, and the short cache TTL.

Approach

• Added sorobanService.getPoolSharePrice(token) as a read-only Soroban simulation.
• Added a small token-scoped cache so dashboard/API consumers do not repeatedly hit RPC for the same value.
• Kept the route behind the existing lender JWT + read:pool checks.
• Refactored aggregate pool stats into a shared helper so /pool/stats and this endpoint use the same utilization calculation.
• Restored the missing transactionRoutes import so backend typecheck can run cleanly.

Security

• Read-only endpoint: no deposit, withdrawal, signing, or transaction submission path is touched.
• Token input is validated before calling Soroban address parsing.
• Cache keys include the token address to avoid cross-token data mixing.
• Authorization matches the existing pool read surface: authenticated lender role plus read:pool scope.

Verification

• npm test -- --runTestsByPath src/__tests__/poolSharePrice.test.ts
• npm test -- --runTestsByPath src/__tests__/poolController.asyncHandler.test.ts src/__tests__/swaggerDocs.test.ts
• npm run typecheck
• git diff --check

[Lucas-FManager]

CI note after re-checking the failing workflow:

• CodeQL and supply-chain checks are passing.
• I re-ran formatting/lint on the backend files changed by this PR locally:
  • npx prettier --check src/app.ts src/config/swaggerSchemas.ts src/controllers/poolController.ts src/routes/poolRoutes.ts src/schemas/poolSchemas.ts src/services/sorobanService.ts src/__tests__/poolSharePrice.test.ts -> passed
  • npx eslint src/app.ts src/config/swaggerSchemas.ts src/controllers/poolController.ts src/routes/poolRoutes.ts src/schemas/poolSchemas.ts src/services/sorobanService.ts src/__tests__/poolSharePrice.test.ts -> passed with warnings only
• The red CI is coming from the shared full-repo lint/format pass, including files outside this PR scope. I am leaving the branch unchanged unless you want the PR to also normalize broader repository formatting.