feat(plugins): import IntelliJ theme plugins (#1184)

Settings › Plugins (gear menu) gets Import Theme from IntelliJ IDE… (theme plugins of the JetBrains IDEs on this machine, the one each IDE uses first) and Import IntelliJ Theme from File… (a Marketplace .jar / .zip or a .theme.json). The host reads the plugin with size limits; the UI converts it with the IntelliJ mapping (moved from scripts/theme to src/features/plugins/intellijTheme.ts, still used by pnpm theme:import-intellij) into one OpenIDEA theme plugin (engines.openidea ^1.0) with all of its themes, installed through the usual install page, and applies the chosen theme.

Theme pickers separate each plugin's themes, and Quick Switch Scheme › Theme previews the theme under the pointer or keyboard after 500 ms and restores the selected one when closed without a choice.

Co-authored-by: ldg030201 <[email protected]>

src/features/plugins/PluginsPage.module.css

@@ -384,3 +384,63 @@
   padding: 12px 16px;
   overflow: auto;
 }
+
+/* Import Theme from IntelliJ IDE */
+.intellijThemes {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  min-width: 0;
+  padding: 14px;
+}
+.intellijThemes > p {
+  margin: 0;
+}
+/* As tall as its rows (the list sizes them), scrolling past seven. */
+.intellijThemesList {
+  max-height: 316px;
+  padding: 4px 0;
+  border: 1px solid var(--border);
+  border-radius: var(--radius-control);
+}
+.intellijThemesStatus {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  padding: 8px 10px;
+  color: var(--fg-muted);
+}
+.intellijTheme {
+  display: flex;
+  flex: 1;
+  align-items: center;
+  gap: 8px;
+  min-width: 0;
+}
+.intellijTheme > .muted {
+  flex-shrink: 0;
+  font-size: var(--fs-small);
+}
+.intellijPlugin {
+  display: flex;
+  flex: 1;
+  align-items: center;
+  gap: 8px;
+  align-self: stretch;
+  min-width: 0;
+}
+/* A line above each plugin but the first, as in IDEA's Theme list. */
+.intellijPluginNext {
+  border-top: 1px solid var(--border);
+}
+.intellijPluginName {
+  overflow: hidden;
+  color: var(--fg-secondary);
+  font-weight: 600;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.intellijPluginIde {
+  flex-shrink: 0;
+  margin-left: auto;
+}