fix(api): combine range conditions on the same field in list queries

[wakqasahmed]

Description

This fixes list filters that set two bounds on the same field, like created[gte] with created[lte], so both bounds are applied instead of only the last one. Database.Query used to spread each parameter's filter into one object, which made { created: { $lte } } replace { created: { $gte } }. It now merges operator conditions that target the same field, and keeps the old replace behaviour for plain equality values.

Fixes #179

Type of Change

• Bug fix
• New feature
• Breaking change
• Refactoring
• Documentation

How Was This Tested?

• Unit tests
• Integration tests
• Manual testing

I added apps/api/src/__tests__/Database.spec.ts, which checks the filter Query passes to the model's find. It covers a gte/lte range on created alongside an equality on another field, a gt/lt range combined with a startAfter cursor, and two equality conditions on one field, where the last one still wins. The first two failed on main and pass with this change. I also ran npx nx test api (33 suites, 506 tests passing), npm run format:check, eslint on the changed files and npx nx build api.

Screenshots (if applicable)

N/A

Checklist

• Self-reviewed my code
• No new warnings
• Existing tests still pass
• Breaking changes are documented above