Once a project/session tab was open, the home chooser (Sessions/Projects
segmented control) was hidden and only reachable by closing every tab — no
way back to the Projects view to open another project.
Add a ⌂ Home button to the tab bar that overlays the chooser on top of the
open tabs (homeForced flag; updateHomeView shows home when no tab OR forced,
hiding the terminal panes). Clicking ⌂ again, clicking a tab (activate resets
homeForced), or opening another session/project dismisses the overlay.
Closing the last tab resets the flag. The button highlights while active.
Tests: +3 (tabs.test.ts). Full suite 415 green; both typechecks clean;
verified in-browser (open tab → ⌂ → Projects panel reachable → ⌂ → terminal).
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