* fix(ds): keep DS::Menu/Popover panels anchored across Turbo morphs
The app refreshes pages via Turbo morph (`turbo_refreshes_with method:
:morph`), and same-page account actions (disable, exclude, set-default,
etc.) trigger one. Two bugs in the shared floating-ui controllers surface
as a result:
- The panel's `position: fixed` only ever existed as a JS-applied inline
style. Idiomorph resets every menu/popover's `style` attribute to match
the server-rendered markup (which has none), silently stripping
`position: fixed` from every panel on the page. The next dropdown/
popover opened before floating-ui's async recompute lands briefly
renders in normal flex flow, shoving its own trigger sideways and
making computePosition anchor to that phantom position instead of the
real button. Fix: make `position: fixed` part of the static markup so
it can never be stripped.
- `this.show` was a plain instance property. Because the morph preserves
the Stimulus controller in place (stable-id turbo frame), `this.show`
doesn't reset when idiomorph re-closes the content element, so it can
desync from the DOM and swallow the next click. Fix: derive `show` from
the content element's own class instead of tracking it separately.
Reproduced and verified against the actual Turbo/Stimulus/floating-ui
pipeline in an isolated harness before and after the fix.
* test(ds): add regression coverage for menu/popover reopen-after-morph
Simulates what idiomorph does to an open panel on a same-page Turbo
morph — resets the content element's class back to the always-hidden
server-rendered markup and strips the JS-applied inline style, without
going through toggle()/close(). Verified against the pre-fix controllers
that this fails without the DOM-derived `show` getter.
