Subshell 0.77.0-beta.6

Sixth public beta of Subshell.

Highlights:

• Returning to Home or a community from a post keeps your place in the feed; cached feeds revalidate on first entry and again after fifteen minutes.
• Internal restructuring of app state into focused components and removal of unused screens, with no intended visible changes.
• Same changes as beta.5, republished so the in-app update check can offer it.