feat: enhance StellarLend documentation, setup guide, and developer workflow

[Tobiloba0]

What Changed

• Code:Fixed TypeScript compilation errors across the api workspace by:
  • Adding missing next: NextFunction parameters to Express handlers in:
  • debtToken.controller.ts
  • lending.controller.ts
  • rebalancing.controller.ts
  • Resolving a naming/call mismatch in portfolio.controller.ts by renaming the import to buildHealthFactorMonitor and updating its usage.
  • Extending WebSocket types in index.ts to include analytics subscribe/unsubscribe messages (subscribe_analytics / unsubscribe_analytics) and corresponding server messages.
• Behavior: Restores successful TypeScript builds and enables clients to request analytics subscriptions over the API WebSocket protocol.

Why

• The repository's api build was failing due to handler functions calling next(error) without declaring the next parameter, and WebSocket client message types lacked analytics subscription messages.
• These issues prevented workspace builds and blocked development & testing on branch fix/issue-358. The changes fix the root causes so the API compiles cleanly and correctly types analytics WS messages.

Testing

• Unit tests updated or added
• Relevant local checks passed — ran cd api && npm run build and npm --workspaces run build --if-present (both succeeded)
• Manual verification completed when needed — verified TypeScript compilation and workspace builds

Closes #358

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[Tobiloba0]

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