feat(plugins): Theme plugin template, theme docs and IntelliJ theme import (#54)

Per the maintainer's decision for #24, no third-party themes are bundled; instead a theme plugin template and docs let the community port themes (IntelliJ also ships few themes, the rest are plugins).
- templates/theme-plugin: manifest-only plugin with an original example (Harbor Night) covering every UI token and an editor scheme (.icls equivalent).
- docs/plugins/themes.md: format, IntelliJ / VS Code porting tables, generated token reference (pnpm gen:theme-docs); drift test fails when tokens.css and the template/reference disagree.
- pnpm theme:import-intellij: dependency-free converter for IntelliJ .theme.json (+ .icls).
- Plugin host: themes may name an editor-scheme merged over the theme; comments allowed in theme files.
- Fixes: a plugin theme's kind now switches the light/dark base; plugin themes go in their own stylesheet so the Appearance accent and editor scheme still layer on top.
Verified: ide-plugin tests, vitest (44), in-app on macOS: installed the template from disk, applied Harbor Night (dark base + teal accent over Islands Light), back to default restored the light theme.

Claude-Session: https://claude.ai/code/session_01VUYsdXA2nkF5v6zsC93dpn

src/features/plugins/__tests__/plugins.test.tsx

@@ -7,10 +7,12 @@ import type { PluginInfo } from "@/bindings";
 import { _setActiveEditor } from "@/editor/api";
 import { executeAction, getAction } from "@/platform/actions";
 import { provideNotificationService, type NotificationService } from "@/workbench/contributions";
+import { applyThemeAttributes, useThemeOverride } from "@/workbench/theme";
 import { createMemoryPluginsBackend, sampleCatalog, setPluginsBackend, type PluginsBackend } from "../backend";
 import {
   applyPluginTheme,
   applyTextToActiveEditor,
+  PLUGIN_THEME_STYLE_ID,
   handlePluginEvent,
   pluginActionId,
   pluginActions,
@@ -160,20 +162,40 @@ describe("store", () => {
 });
 
 describe("bridge events", () => {
-  it("applies theme tokens as CSS variables and removes them again", () => {
+  it("applies theme tokens as a stylesheet and removes it again", () => {
     const root = document.documentElement;
+    const sheet = () => document.getElementById(PLUGIN_THEME_STYLE_ID)?.textContent ?? null;
     applyPluginTheme({
       pluginId: "p",
       theme: { id: "t", name: "T", kind: "dark", tokens: { "--bg-app": "#002b36", "--evil": "red; x: y", bad: "1" } },
     });
-    expect(root.style.getPropertyValue("--bg-app")).toBe("#002b36");
-    expect(root.style.getPropertyValue("--evil")).toBe("");
+    expect(sheet()).toContain("--bg-app: #002b36;");
+    expect(sheet()).toContain("color-scheme: dark;");
+    expect(sheet()).not.toContain("evil");
+    expect(sheet()).not.toContain("bad");
     expect(root.dataset.pluginTheme).toBe("p/t");
     applyPluginTheme(null);
-    expect(root.style.getPropertyValue("--bg-app")).toBe("");
+    expect(sheet()).toBeNull();
     expect(root.dataset.pluginTheme).toBeUndefined();
   });
 
+  it("switches the built-in base to the theme's kind and restores it", () => {
+    const root = document.documentElement;
+    useThemeOverride.setState({ theme: "dark-hc" });
+    applyThemeAttributes("dark-hc", root);
+    expect([root.dataset.theme, root.dataset.contrast]).toEqual(["dark", "high"]);
+    applyPluginTheme({ pluginId: "p", theme: { id: "l", name: "L", kind: "light", tokens: { "--accent": "#123456" } } });
+    expect([root.dataset.theme, root.dataset.contrast]).toEqual(["light", undefined]);
+    expect(root.dataset.pluginThemeKind).toBe("light");
+    // The appearance runtime re-applying the built-in theme keeps the plugin's base.
+    applyThemeAttributes("dark-hc", root);
+    expect(root.dataset.theme).toBe("light");
+    applyPluginTheme(null);
+    expect([root.dataset.theme, root.dataset.contrast]).toEqual(["dark", "high"]);
+    expect(root.dataset.pluginThemeKind).toBeUndefined();
+    useThemeOverride.setState({ theme: null });
+  });
+
   it("inserts at the cursor and replaces selections", () => {
     const v = editor("hello world", 6, 11);
     handlePluginEvent({ type: "replaceSelection", pluginId: "p", text: "there" });

src/features/plugins/bridge.ts

@@ -1,13 +1,14 @@
 /**
  * Glue between backend plugins and the workbench: plugin commands become
- * actions, editor requests are applied to the active editor, theme overrides
- * become CSS variables, notifications become balloons.
+ * actions, editor requests are applied to the active editor, the selected
+ * theme becomes a stylesheet of CSS variables, notifications become balloons.
  */
 import { EditorSelection } from "@codemirror/state";
 import type { ActiveTheme, PluginEvent, PluginInfo } from "@/bindings";
 import { activeEditor, useEditorRegistry } from "@/editor/api";
 import { registerAction, type Action } from "@/platform/actions";
 import { notifications } from "@/workbench/contributions";
+import { applyThemeAttributes, currentThemeId, syncWindowBackground } from "@/workbench/theme";
 import { pluginsBackend } from "./backend";
 import { refreshPlugins, runPluginCommand, usePlugins } from "./store";
 
@@ -64,23 +65,44 @@ export function syncPluginActions(): () => void {
 
 // --- theme ------------------------------------------------------------------
 
-let appliedTokens: string[] = [];
+export const PLUGIN_THEME_STYLE_ID = "openidea-plugin-theme";
 
-/** Applies a plugin theme's token overrides as inline CSS variables on :root (null clears). */
+/** Stylesheet for a plugin theme. Its selector outranks every built-in theme block. */
+export function pluginThemeCss(theme: ActiveTheme["theme"]): string {
+  const kind = theme.kind === "light" ? "light" : "dark";
+  const decls = [`  color-scheme: ${kind};`];
+  for (const [name, value] of Object.entries(theme.tokens)) {
+    // Backend validates; keep the guard so a malformed payload can't inject declarations.
+    if (!/^--[a-z0-9-]+$/.test(name) || value == null || /[;{}<>\\]/.test(value)) continue;
+    decls.push(`  ${name}: ${value};`);
+  }
+  return `:root[data-plugin-theme]:not([data-plugin-theme=""]) {\n${decls.join("\n")}\n}\n`;
+}
+
+/**
+ * Applies a plugin theme (null restores the built-in one): its tokens as a
+ * stylesheet over the built-in light or dark base named by its `kind`. A
+ * stylesheet rather than inline styles, so the accent picked in Settings ›
+ * Appearance and the editor colour scheme still layer on top.
+ */
 export function applyPluginTheme(theme: ActiveTheme | null, root: HTMLElement = document.documentElement) {
-  for (const name of appliedTokens) root.style.removeProperty(name);
-  appliedTokens = [];
+  const doc = root.ownerDocument;
+  doc.getElementById(PLUGIN_THEME_STYLE_ID)?.remove();
+  const had = root.dataset.pluginTheme !== undefined;
   if (!theme) {
     delete root.dataset.pluginTheme;
-    return;
+    delete root.dataset.pluginThemeKind;
+    if (had) applyThemeAttributes(currentThemeId(), root);
+  } else {
+    const style = doc.createElement("style");
+    style.id = PLUGIN_THEME_STYLE_ID;
+    style.textContent = pluginThemeCss(theme.theme);
+    doc.head.appendChild(style);
+    root.dataset.pluginTheme = `${theme.pluginId}/${theme.theme.id}`;
+    root.dataset.pluginThemeKind = theme.theme.kind === "light" ? "light" : "dark";
+    applyThemeAttributes(currentThemeId(), root);
   }
-  for (const [name, value] of Object.entries(theme.theme.tokens)) {
-    // Backend validates; keep the guard so a malformed payload can't inject declarations.
-    if (!/^--[a-z0-9-]+$/.test(name) || value == null || /[;{}<>]/.test(value)) continue;
-    root.style.setProperty(name, value);
-    appliedTokens.push(name);
-  }
-  root.dataset.pluginTheme = `${theme.pluginId}/${theme.theme.id}`;
+  if (had || theme) syncWindowBackground();
 }
 
 export function trackPluginTheme(): () => void {