enhance(ui): use normal line-height for buttons and selection dropdowns (#39796)

The legacy Fomantic `line-height: 1` on buttons made ellipsized button
text clip descenders like `g` letters, like in the PR target branch
selector. Selection dropdowns were 3px taller than the inputs and
buttons next to them because their padding assumed `line-height: 1em`.

- Buttons and selection dropdowns use `--line-height-default` with
smaller vertical padding, `min-height` keeps their sizes for every font
including CJK
- Remove overrides that only compensated for the old values and dropdown
declarations that never applied
- Label-edit and push-mirror modals use regular-size action buttons like
all other modals

web_src/css/modules/modal.css

@@ -111,7 +111,7 @@ like "small" and "mini" are still kept for the HTML elements, these can be clean
   display: inline-flex;
   gap: var(--gap-inline);
   align-items: center;
-  padding: 10px 12px 10px 10px;
+  padding-inline: 10px 12px;
   margin-left: 0.75em;
   margin-right: 0;
 }