Fix/stats webhook improvements

[Mac-5]

Summary

closes #357
closes #358
closes #359
closes #360

Issue 1 — Stats: feeApr from pool fees
stats.worker.ts: replaced the approximation volume24h × (feeTier/1_000_000) with a sum of actual swap.feeAmount fields from 24h swaps, multiplied by the token price, then annualised. Tests updated with feeAmount on mock swaps and two new assertions verifying the real-fee-based result.

Issue 2 — Webhooks: large_swap threshold from env
webhooks.service.ts: largeSwapUsd default now reads LARGE_SWAP_THRESHOLD_USD from the environment (parseFloat(process.env.LARGE_SWAP_THRESHOLD_USD ?? '10000')). Explicit caller value still takes precedence.

Issue 3 — Webhooks: retry failed webhook deliveries

• webhook.processor.ts: WEBHOOK_RETRY_ATTEMPTS is now configurable via process.env.WEBHOOK_RETRY_ATTEMPTS (default 3). Added retryFailedDeliveries(webhookId) which fetches failed BullMQ jobs and calls .retry() on matching ones.
• webhooks.service.ts: retryDeliveries(webhookId, ownerWallet) verifies ownership then delegates to the worker.
• webhooks.controller.ts: POST /webhooks/:id/retry endpoint added.

Issue 4 — Webhooks: webhook signature HMAC verification
webhook.types.ts: verifyWebhookSignature(body, signature, secret) exported — uses timingSafeEqual with a length pre-check and guards against empty/invalid inputs. POST /webhooks/verify-signature endpoint exposed in the controller.

Related issue

• Closes #

Type of change

• Bug fix
• New feature
• Docs update
• Chore / refactor

Checklist

• CI passes (lint + tests + build)
• Self-reviewed the diff
• Added or updated tests where relevant
• Docs updated if needed