feat: add confirmed Take down stack action with optional volume removal (#1599)

* feat: add confirmed Take down stack action with optional volume removal

Expose Take down in the stack header and sidebar with a confirmation dialog
that runs compose down while keeping the stack definition on disk. Optional
volume removal is gated by node capability and stack:deploy permission, with
remote gateway preflight before proxying removeVolumes requests.

Closes #1582

* fix: reset take-down volume checkbox when dialog closes

* test: align getStackMenuVisibility assertions with showTakeDown key

getStackMenuVisibility now returns a fifth lifecycle flag, showTakeDown,
but three exhaustive toEqual assertions still listed only the prior four
keys and failed. Add the expected showTakeDown value to each: true for
the partial and exited running-stack cases, false for the self stack.

* test: cover Take down visibility for running non-self stacks

The getStackMenuVisibility assertions exercised the partial and exited
branches and the self-stack guard, but not the raw === 'running' literal
that drives showTakeDown for a normal running stack. Add a case so a
regression dropping 'running' from that check is caught.

* fix: drop Take down from header overflow and wire activity shortcut

Remove duplicate Take down from More actions.

Keep inline button when running, sidebar menu, and Cmd+ArrowDown.

Record stack_taken_down in activity on successful POST /down.

docs/features/sidebar.mdx

@@ -119,6 +119,7 @@ Shortcuts fire on the currently selected stack. They are blocked while a text in
 | <kbd>Ctrl</kbd>+<kbd>.</kbd> | Stop | Stack is running |
 | <kbd>Ctrl</kbd>+<kbd>R</kbd> | Restart | Stack is running |
 | <kbd>Ctrl</kbd>+<kbd>↑</kbd> | Update images | Stack is running |
+| <kbd>Ctrl</kbd>+<kbd>↓</kbd> | Take down | Stack has been deployed (opens confirmation) |
 | <kbd>Ctrl</kbd>+<kbd>Backspace</kbd> | Delete | Stack exists |
 
 On macOS, use <kbd>Cmd</kbd> in place of <kbd>Ctrl</kbd>.