Support the mouse in the branch popup

A click on a branch switches to it, the wheel moves the selection, a click
outside closes the popup. The popup is hit-tested by its own position, as it
is drawn after zone.Scan.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/actions.md

@@ -218,8 +218,10 @@ branches.
 | `enter` | Switch to the selected branch |
 | `esc` | Close |
 
-Mouse and all other keys are ignored while the popup is open. A header
-selection switches the superproject.
+Mouse: a click on a branch switches to it (like `enter`), the wheel moves the
+selection, a click outside the popup closes it; a click on the title, the
+search line or an empty row does nothing. Everything else is ignored while the
+popup is open. A header selection switches the superproject.
 
 ### Effect
 

docs/architecture.md

@@ -28,7 +28,7 @@ internal/tui/                 Bubble Tea application
   app.go                      root model: layout, message routing, loading
   keys.go                     key bindings (also feed the help view)
   restore.go, switch.go       restore / switch flows; a switch reuses restoreState
-  overlay.go                  draws the picker centered over the finished view
+  overlay.go                  draws the picker over the finished view at the position the picker reports
   msgs.go                     tree/status/fetch/change messages
   refresh.go                  reloader: one load per key, coalesced reruns
   theme/                      colors, glyphs, issue words, change letters, level styles

docs/decisions.md

@@ -376,7 +376,9 @@ restores below, without staging.
   list itself uses none; `f` refreshes remote branches.
 - *Popup.* The first overlay: drawn over the finished view (after
   `zone.Scan`, so no zone marker is cut); the keys go to the picker while it
-  is open. The backdrop is dimmed: stripped of its styles and drawn in
+  is open, and so does the mouse: the popup remembers where it was drawn and
+  tests clicks itself (bubblezone can't see it, it is drawn after the scan).
+  A click on a branch switches, like `enter`; a click outside closes. The backdrop is dimmed: stripped of its styles and drawn in
   `Backdrop`, an adaptive 256-color grey (238 dark / 252 light). `Muted`
   (ANSI 8) was too bright to set the popup apart, and ANSI faint (SGR 2) is
   ignored by some terminals. Like `Bar` and `Selected` it carries no meaning,

docs/ux-guide.md

@@ -353,6 +353,9 @@ where the palette can't be shown, see [Key bar and palette](#key-bar-and-palette
 - Click a row: select it. Click the header: select the superproject.
 - Click `▸` / `▾`: select and toggle.
 - Scroll wheel: move the selection.
+- In the [branch popup](#switch-branch): click a branch to switch to it,
+  wheel to move, click outside to close. The popup is hit-tested by its own
+  position, not with bubblezone, since it is drawn after `zone.Scan`.
 
 ## Accessibility and terminals