Prevent reauthentication retry storms

[ClaudiuSchuster]

Summary

• prevent status polling from creating Proton backend sessions before the managed mount is ready
• persist login-endpoint rate limiting without confusing it with metadata or file-operation 429 responses
• restore the complete reauthorization menu label and make the red Overview banner keyboard- and pointer-activatable
• release the fixes as PDrive 0.8.1 and refresh the current Arch package references

Verification

• git diff --check
• make check
• Super-Linter 8.7.0
• setup-wizard and full GTK widget suites on isolated Broadway displays
• Ubuntu 24.04 and Arch Linux container smoke tests
• Arch 0.8.1-1 package build, metadata inspection, container installation and installed-file probes
• Linux Mint Cinnamon/X11 desktop preflight: 15/15 automated gates

Release boundary

Arch Linux remains a release-candidate target. Its clean Cinnamon/X11 baseline was established with 0.8.0-1; this patch candidate repeats repository, container and native-package gates without claiming a new clean-desktop run. The final public package will be rebuilt from the exact squash-merged main commit.