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/header.css

@@ -107,7 +107,7 @@ h4.ui.header {
 
 /* the default ".ui.attached.header > .ui.right" is only able to contain "tiny" buttons, other buttons are too large */
 .ui.attached.header > .ui.right .ui.tiny.button {
-  padding: 6px 10px;
+  padding-inline: 10px;
   font-weight: var(--font-weight-normal);
 }