Fix start menu width expansion

[themartiano]

Summary

• keep dynamic storage detail text within the fixed 600-point start-menu layout
• truncate clickable folder paths in the middle while preserving their full tooltip and accessibility value
• add an AppKit regression test for long paths, low-space warnings, and storage errors

Testing

• swift test --disable-sandbox (161 tests across 40 suites)
• make app
• runtime visual verification with the active low-space warning: 600 x 760 points
• make test passes through the Swift and QEMU contract suites, then hits a pre-existing main-branch mismatch: qemu-persistent-storage.test.sh expects QEMU 10.2.50 while main stages QEMU 11.1.1