#732 fix: restore box-shadow visibility for Sidekick action bar

[rockygeekz]

Fixes #732

Summary
This change restores the Sidekick action bar's box-shadow rendering that regressed after PR #720 introduced repositioning and new layout wrappers.

What changed

• Moved the --sidekick-box-shadow usage out of the inner .action-bar and applied it on the plugin-action-bar host.
• Added fallback box-shadow values to ensure visibility even if the CSS variable is missing.
• Fixed a CSS syntax error in action-bar.js (color: var(--spectrum2-sidekick-color)).

Why
After PR #720, the inner element receiving the shadow became clipped due to transform/clip-path stacking. Applying the shadow on the host element restores the intended elevation.

Verification

• Verified getComputedStyle(plugin-action-bar).boxShadow returns non-none.
• Confirmed that the inner .action-bar no longer needs the shadow.
• Tested on a local Sidekick sandbox page (custom hosted AEM template) to confirm the shadow renders correctly.

Files changed

• plugin-action-bar.css.js
• dialog-wrapper.css.js
• action-bar.js

No breaking changes.