[StudentWeis]

Summary

Center the About content horizontally and vertically below its header, including the update status/action row.

Linked Issue

Closes #306

Changes

• Use remaining-height flex sizing and auto margins to center the content while retaining overflow scrolling.
• Center update status/actions independently of the managed-install hint.
• Add production-view geometry and short-window scrolling regression coverage; extract status text mapping to meet the Clippy function-length limit.

Testing

• scripts/precheck.sh passes locally (Python 3.13 on PATH): 83 script tests and 761 Rust tests passed, plus resource, Clippy and documentation checks.
• New / updated tests cover the change
• Confirmed the regression test failed on the previous vertical alignment and passes after the fix.
• Native-window screenshot acceptance has not been performed. Existing block v0.1.6 future-compatibility warning remains.

Self-Check

• PR title follows Conventional Commits
• No hardcoded user-facing strings — existing localization keys retained
• Errors defined with thiserror (no new error types)
• No unrelated changes mixed in