Initialize Harmness Browser JetBrains plugin skeleton

- Gradle + Kotlin + IntelliJ Platform SDK build
- JCEF embedded browser tool window with configurable start URL
- Settings page (Tools > Harmness Browser)
- JS<->Java bridge scaffold (window.harmnessBridge)
- Vite + React + TypeScript web scaffold for embedded page
- README: build, register, upload to Marketplace, install guide

src/main/resources/META-INF/plugin.xml

@@ -0,0 +1,47 @@
+<idea-plugin>
+    <id>com.harmness.toolwindow</id>
+    <name>Harmness Browser</name>
+    <vendor>harmness</vendor>
+
+    <description>
+        Embed a configurable browser panel (e.g. a local Harmness instance) directly inside
+        JetBrains IDE sidebars. Enables seamless AI-assisted coding inside PyCharm / IntelliJ
+        IDEA without switching to a separate browser window.
+    </description>
+
+    <!--
+        IDE version compatibility:
+        sinceBuild / untilBuild 控制插件兼容的 IDE 版本范围。
+        这里要求 2024.2 及以上、2024.3.* 及以下。
+        如需支持更老版本，请参考 https://plugins.jetbrains.com/docs/intellij/build-number-ranges.html
+    -->
+    <idea-version since-build="242" until-build="243.*"/>
+
+    <!-- 依赖 platform -->
+    <depends>com.intellij.modules.platform</depends>
+
+    <!-- 工具窗口扩展点 -->
+    <extensions defaultExtensionNs="com.intellij">
+        <toolWindow
+            id="Harmness Browser"
+            icon="/icons/harmness.svg"
+            factoryClass="com.harmness.toolwindow.HarmnessToolWindowFactory"
+            anchor="right"
+            condition="class#==com.intellij.ui.jcef.JBCefApp"
+        />
+
+        <!-- 插件设置页：Settings | Tools | Harmness Browser -->
+        <applicationConfigurable
+            parent="tools"
+            instance="com.harmness.toolwindow.HarmnessSettingsConfigurable"
+            id="com.harmness.toolwindow.HarmnessSettingsConfigurable"
+            displayName="Harmness Browser"/>
+
+        <!-- 持久化组件 -->
+        <applicationService
+            serviceImplementation="com.harmness.toolwindow.SettingsState"/>
+
+        <applicationService
+            serviceImplementation="com.harmness.toolwindow.WindowFocusService"/>
+    </extensions>
+</idea-plugin>