e0m2: Small tweaks

[RandomBrushes]

Description of Changes

---

• added some geometry on a ceiling
• texture alignment tweaks
• turned a time-based trigger into a trigger brush

Latter is the only gameplay-related change and serves to avoid player-confusion on why suddenly there are knights rushing in.

Visual Sample

Checklist

---

• [x] I have read the LibreQuake contribution guidelines
• [x] I have thoroughly tested my changes to the best of my ability
• [x] I confirm I have not contributed anything that would impact LibreQuake's licensing and usage
• [ ] This Pull Request fixes a critical issue that should be reviewed and merged as soon as possible

[MotoLegacy]

Hi, keep in mind in about a weeks time we will have to have everyone follow the contributing guidelines: https://github.com/lavenderdotpet/LibreQuake/blob/main/CONTRIBUTING.md

Will review when I have the chance to playtest, thanks!

[MotoLegacy]

Please let us know when you are comfortable with a merge.

[RandomBrushes]

Please let us know when you are comfortable with a merge.

well, I am ;-)