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

templates/repo/issue/labels/label_edit_modal.tmpl

@@ -57,11 +57,11 @@
 		</form>
 	</div>
 	<div class="actions">
-		<button type="button" class="ui small basic cancel button">
+		<button type="button" class="ui basic cancel button">
 			{{svg "octicon-x"}}
 			{{ctx.Locale.Tr "cancel"}}
 		</button>
-		<button type="button" class="ui primary small approve button">
+		<button type="button" class="ui primary approve button">
 			{{svg "fontawesome-save"}}
 			{{ctx.Locale.Tr "save"}}
 		</button>

templates/repo/settings/push_mirror_sync_modal.tmpl

@@ -14,11 +14,11 @@
 			<input id="push-mirror-edit-interval" name="push_mirror_interval" class="tw-w-auto">
 		</div>
 		<div class="actions">
-			<button type="button" class="ui small basic cancel button">
+			<button type="button" class="ui basic cancel button">
 				{{svg "octicon-x"}}
 				{{ctx.Locale.Tr "cancel"}}
 			</button>
-			<button type="submit" class="ui primary small approve button">
+			<button type="submit" class="ui primary approve button">
 				{{svg "fontawesome-save"}}
 				{{ctx.Locale.Tr "save"}}
 			</button>