refactor: standardize undefined handling for categories

[hanna-skryl]

Closes #518

This refactor standardizes the handling of categories as undefined throughout the CLI pipeline until conversion to the GQL report. Previously, an empty array was assigned by default in middlewares, leading to inconsistencies with CoreConfig where categories are optional.

By removing the default empty array, categories remain undefined unless explicitly provided. This update improves type consistency, ensuring that categories are only included in the final report if defined. When no categories are provided, the JSON report omits the categories field, and the Markdown report summary table indicates that there are 0 categories.

[github-actions]

Code PushUp

🤨 Code PushUp report has both improvements and regressions – compared target commit cc98195 with source commit 61d49ea.

🕵️ See full comparison in Code PushUp portal 🔍

🏷️ Categories

🏷️ Category	⭐ Previous score	⭐ Current score	🔄 Score change
Performance	🟡 54	🟡 52
Code coverage	🟡 90	🟡 90
Custom checks	🟡 67	🟡 67	–
Security	🟡 88	🟡 88	–
Updates	🟡 76	🟡 76	–
Accessibility	🟢 91	🟢 91	–
Best Practices	🟢 100	🟢 100	–
SEO	🟡 61	🟡 61	–
Bug prevention	🟢 100	🟢 100	–
Code style	🟢 100	🟢 100	–

👍 1 group improved, 👎 1 group regressed, 👍 5 audits improved, 👎 1 audit regressed, 14 audits changed without impacting score

🗃️ Groups

🔌 Plugin	🗃️ Group	⭐ Previous score	⭐ Current score	🔄 Score change
Lighthouse	Performance	🟡 54	🟡 52
Code coverage	Code coverage metrics	🟡 90	🟡 90

18 other groups are unchanged.

🛡️ Audits

🔌 Plugin	🛡️ Audit	📏 Previous value	📏 Current value	🔄 Value change
Lighthouse	Largest Contentful Paint	🟨 3.0 s	🟨 3.3 s
Lighthouse	First Contentful Paint	🟨 3.0 s	🟨 2.7 s
Lighthouse	Speed Index	🟥 6.6 s	🟥 6.4 s
Lighthouse	Time to Interactive	🟥 17.7 s	🟥 16.2 s
Code coverage	Function coverage	🟩 92.4 %	🟩 92.4 %
Code coverage	Line coverage	🟩 90.4 %	🟩 90.4 %
Lighthouse	Avoids enormous network payloads	🟩 Total size was 1,818 KiB	🟩 Total size was 1,813 KiB
Lighthouse	JavaScript execution time	🟥 11.0 s	🟥 9.4 s
Lighthouse	Metrics	🟩 100%	🟩 100%
Lighthouse	Minimizes main-thread work	🟥 18.7 s	🟥 19.2 s
Lighthouse	Eliminate render-blocking resources	🟥 Potential savings of 1,140 ms	🟥 Potential savings of 720 ms
Lighthouse	Initial server response time was short	🟩 Root document took 590 ms	🟩 Root document took 370 ms
Lighthouse	Server Backend Latencies	🟩 230 ms	🟩 100 ms
Lighthouse	Uses efficient cache policy on static assets	🟨 27 resources found	🟨 27 resources found
Lighthouse	Total Blocking Time	🟥 6,850 ms	🟥 6,750 ms
Lighthouse	Max Potential First Input Delay	🟥 2,850 ms	🟥 2,790 ms
Lighthouse	Network Round Trip Times	🟩 70 ms	🟩 20 ms
Lighthouse	Avoids an excessive DOM size	🟥 2,245 elements	🟥 2,241 elements
JS Packages	Outdated NPM dev dependencies.	🟨 39 outdated package versions (26 major, 10 minor, 2 patch, 1 prerelease)	🟨 40 outdated package versions (26 major, 10 minor, 3 patch, 1 prerelease)
Code coverage	Branch coverage	🟨 84.8 %	🟨 84.8 %

493 other audits are unchanged.