feat(actions): Add artifact preview in Actions run view (#36754)

Closes https://github.com/go-gitea/gitea/issues/33579.

Adds browser previews for Actions artifacts. Selecting an artifact opens
its file browser; selecting a file renders it in the same tab. The ZIP
download remains available separately.

Previews require sign-in and read access to the run. Text, image and PDF
files are supported; rendered HTML and JavaScript run in a sandboxed
frame and are labeled as automatically generated. The frame loads files
from a signed link that expires after an hour, because its requests
carry no session cookie. `[actions] ARTIFACT_PREVIEW_MAX_SIZE` limits
total previewable artifact size (`0` disables previews; `-1` removes the
limit); individual files also follow `[ui] MAX_DISPLAY_FILE_SIZE`.

<img width="1803" height="913" alt="image"
src="https://github.com/user-attachments/assets/a38fd704-2244-44fa-9181-c695ecbe0276"
/>

Docs: https://gitea.com/gitea/docs/pulls/533

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

web_src/css/actions.css

@@ -94,3 +94,61 @@
   order: 2;
   margin-left: auto;
 }
+
+.action-view-header {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  margin-top: 8px;
+  min-height: 50px; /* reserve the back link and title height so the body does not shift when the run data arrives */
+}
+
+.action-view-back {
+  display: inline-flex;
+  align-items: center;
+  align-self: flex-start;
+  gap: 4px;
+  font-size: 13px;
+  color: var(--color-text-light-1);
+  text-decoration: none;
+}
+
+.action-view-back:hover {
+  color: var(--color-text);
+  text-decoration: none;
+}
+
+.action-info-summary {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+}
+
+.action-info-summary-title {
+  display: flex;
+  align-items: center;
+  gap: 0.5em;
+}
+
+.action-info-summary-title-text {
+  font-size: 20px;
+  margin: 0;
+  overflow-wrap: anywhere;
+}
+
+.action-info-summary-title-index {
+  font-size: 20px;
+  color: var(--color-text-light-2);
+  flex: 1;
+}
+
+.action-info-summary .ui.button {
+  margin: 0;
+  white-space: nowrap;
+}
+
+.ui.vertical.menu .artifact-preview-item {
+  padding-left: calc(1em + var(--depth, 0) * 1.25em);
+}