feat(analytics): add TVL endpoint for pending stakes aggregation

[phertyameen]

Summary

Adds a new endpoint that aggregates a user's active Portfolio Total Value
Locked (TVL) by summing all stakes where the underlying call is still PENDING.

Endpoint

GET /analytics/:userAddress/tvl

Changes

• dto/tvl.dto.ts new TotalValueLockedResponseDto with totalValueLocked,
  pendingStakesCount, and userAddress fields
• analytics.service.ts new getTotalValueLocked() method using a TypeORM
  QueryBuilder aggregate query joined on the Call relation
• analytics.controller.ts new GET endpoint with full Swagger documentation
• analytics.service.tvl.spec.ts unit tests covering happy path, zero stakes,
  and null DB response edge case

Testing

• Unit tests pass (npm run test)
• Swagger UI reflects new endpoint
• Manually verified with a wallet address that has pending stakes

Closes #116

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