fix(webhooks): correct keyset cursor lookup for table-qualified columns

[rexx010]

applyKnexKeyset() looked up cursor values by the raw column name (e.g. "e.created_at") but cursors are encoded with plain field names ("created_at"), so keyset comparisons bound to undefined and page 2+ silently came back empty.

Summary

Fixes applyKnexKeyset so table-qualified sort columns (e.g. "e.created_at") correctly resolve against cursor objects, which are always keyed by plain field names — restoring working pagination past page 1 for the webhook events endpoint.

Type of change

• Bug fix
• New feature
• Documentation update
• Refactor / chore
• Smart contract change

Related issue

Closes #888

Changes

• backend/src/utils/paginate.js: applyKnexKeyset now strips a table-alias prefix before reading the cursor object, and skips the seek predicate entirely if the cursor is missing a required field instead of comparing a column to undefined.
• backend/__tests__/webhookService.test.js: fixed the knex mock's join() to actually evaluate where/andWhere/orWhere callbacks and sort rows via orderBy (it previously no-op'd them, so it couldn't exercise real keyset behavior).
• Added a test verifying two pages of equal-created_at events return every row exactly once (no overlap, no gap).

Testing

• Added/updated unit tests
• npx jest __tests__/webhookService.test.js → 23/23 pass
• npx eslint src/utils/paginate.js → clean

Screenshots (if UI change)

N/A — backend-only fix, no UI change.

Checklist

• My code follows the project style
• I've updated docs if needed
• No console errors or warnings
• I've rebased on latest main

[github-actions]

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