enhance(ui): tweak tooltip style and misc fixes (#38524)

Tooltip changes:

- center tooltips over their target (default placement `top` instead of
`top-start`)
- fix the arrow rendering off-center on references narrower than 22px
like 16px icons, caused by tippy's hardcoded 3px arrow padding
- fix arrowed tooltips overlapping their reference by 1px because the
offset distance was derived from the raw arrow option
- tweak tooltip colors and reduce content padding
- fix a Firefox bug where lazily created tooltips would not show on the
first hover, because Firefox skips enter/leave event dispatch when no
such listener existed in the window at the time of the pointer crossing

Other UI tweaks:

- tweak repo sidebar release style
- enhance actions back link
- center step chevron
- add border on workflow graph

<img width="92" height="76" alt="Screenshot 2026-07-21 at 18 07 42"
src="https://github.com/user-attachments/assets/968a51de-e470-48c0-b592-4a207dfcbb63"
/>
<img width="94" height="76" alt="Screenshot 2026-07-21 at 18 07 53"
src="https://github.com/user-attachments/assets/5e8e0ce3-7536-4689-a6ae-9cfb6e867ddb"
/>


<img width="203" height="77" alt="Screenshot 2026-07-19 at 00 14 32"
src="https://github.com/user-attachments/assets/71c16a54-ad14-4636-8af4-e68b3599f1d0"
/>
<img width="309" height="290" alt="Screenshot 2026-07-18 at 23 37 21"
src="https://github.com/user-attachments/assets/29630504-d69a-4e23-978b-41ae6d0bff92"
/>
<img width="151" height="110" alt="Screenshot 2026-07-18 at 23 35 47"
src="https://github.com/user-attachments/assets/b8107602-12f1-4f9b-a3f6-b930af25c9e7"
/>

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/components/ActionRunJobView.vue

@@ -493,7 +493,7 @@ async function hashChangeListener() {
         <SvgIcon
           v-else
           name="octicon-chevron-right"
-          class="tw-mr-2 step-summary-chevron"
+          class="step-summary-chevron"
           :class="{'tw-invisible': !isExpandable(jobStep.status)}"
         />
         <ActionStatusIcon :status="jobStep.status" icon-variant="circle-fill"/>

web_src/js/components/RepoActionView.vue

@@ -132,7 +132,7 @@ onBeforeUnmount(() => {
   <!-- make the view container full width to make users easier to read logs -->
   <div class="ui fluid container">
     <div class="action-view-header">
-      <a v-if="backLink" class="action-view-back silenced" :href="backLink.href">
+      <a v-if="backLink" class="action-view-back" :href="backLink.href">
         <SvgIcon name="octicon-arrow-left" :size="14"/>
         <span>{{ backLink.prefix }} <span class="action-view-back-name">{{ backLink.name }}</span></span>
       </a>
@@ -188,7 +188,7 @@ onBeforeUnmount(() => {
                 </div>
                 <div class="flex-text-block tw-pl-[20px]">
                   <span class="flex-text-inline tw-flex-shrink-0">
-                    <ActionStatusIcon :locale-status="locale.status[attempt.status]" :status="attempt.status" :size="14" class="flex-text-block" icon-variant="circle-fill"/>
+                    <ActionStatusIcon :locale-status="locale.status[attempt.status]" :status="attempt.status" :size="14" icon-variant="circle-fill"/>
                     <span>{{ locale.status[attempt.status] }}</span>
                   </span>
                   <span>•</span>
@@ -364,14 +364,10 @@ onBeforeUnmount(() => {
   gap: 4px;
   font-size: 13px;
   color: var(--color-text-light-1);
+  text-decoration: none;
 }
 
 .action-view-back:hover {
-  color: var(--color-primary);
-}
-
-.action-view-back-name {
-  font-weight: var(--font-weight-bold);
   color: var(--color-text);
 }
 

web_src/js/components/WorkflowGraph.vue

@@ -434,6 +434,7 @@ function onNodeClick(job: GraphNode | ActionsJob, event: MouseEvent) {
   background: var(--color-console-bg);
   gap: var(--gap-block);
   flex-wrap: wrap;
+  border-bottom: 1px solid var(--color-secondary);
 }
 
 .graph-workflow-info {