Fix full-width message layouts

[thomaspblock]

Summary

• Remove fixed-width caps from repo pages and the main desktop message timeline/composer so content uses the available pane width.
• Move message timestamps inline with author names, including system messages and Home inbox detail rows, with subtler timestamp styling.
• Update day divider stacking and loading skeletons to match the full-width message layout.

Test plan

• Pre-commit hooks passed.
• Pre-push full suite passed: desktop/web builds and checks, Rust checks/tests, mobile checks/tests.
• Post-push desktop verification passed: pnpm check && pnpm build.

Made with Cursor

[thomaspblock]

textwidth.mp4