🔧 fix(vscode): worktree 目录配置改用插件自带设置面板，撤销 VS Code 原生配置

上一版误把 worktree 目录模板注册成 VS Code 原生设置（contributes.configuration
+ workspace.getConfiguration），但本插件有自己的设置面板（SettingsModal，存 globalState）。
改为：
- Settings 新增 worktreeDirectory 字段（默认 ~/Sources/worktree/$project_name/$feature_name，
  留空回退默认），贯穿 store/handler/两端 messages/useIssues/App/SettingsModal
- SettingsModal「钩子」分组新增「工作树目录」输入项，走既有 save/load 流程
- handleImplement 改从 getSettings(panel.context).worktreeDirectory 读模板
- 删除 package.json 的 contributes.configuration（meta.ts 为 gitignore 生成物，已本地还原）

deriveSlug / resolveWorktreeDir / ~ 展开 / 绝对路径 / feature/<slug> 逻辑不变。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

vscode/src/settings/store.ts

@@ -86,6 +86,14 @@ export interface Settings {
    * disabled because there's nothing to fast-forward.
    */
   autoBuildBranch: string
+  /**
+   * Directory template for the worktree created when implementing a plan.
+   * Placeholders: `$project_root` (workspace abs path), `$project_name` (its
+   * basename), `$feature_name` (the spec/plan slug). A leading `~` expands to
+   * the user's home dir. Empty string means "use the default
+   * `~/Sources/worktree/$project_name/$feature_name`".
+   */
+  worktreeDirectory: string
   /**
    * Path to a user-provided shell script that runs *after* the extension
    * creates a worktree via `git worktree add`. Empty string means use the
@@ -157,6 +165,7 @@ function defaults(ctx: ExtensionContext): Settings {
     reviewPrompt: readDefaultPrompt(ctx.extensionPath, 'review'),
     devBranch: 'main',
     autoBuildBranch: '',
+    worktreeDirectory: '~/Sources/worktree/$project_name/$feature_name',
     worktreePostCreateScript: '',
     worktreePreRemoveScript: '',
     implTabPreCreateScript: '',
@@ -200,6 +209,11 @@ export function getSettings(ctx: ExtensionContext): Settings {
   const autoBuildBranch = typeof stored.autoBuildBranch === 'string'
     ? stored.autoBuildBranch
     : base.autoBuildBranch
+  // worktree dir template: empty/blank means "use the default template", so
+  // fall back to base (unlike the hook paths below, where '' is meaningful).
+  const worktreeDirectory = typeof stored.worktreeDirectory === 'string' && stored.worktreeDirectory.length > 0
+    ? stored.worktreeDirectory
+    : base.worktreeDirectory
   // worktree hook script paths: '' is meaningful (= "use default
   // .spx/worktree-*.sh"), so don't coerce. Non-string legacy values fall
   // back to ''. The hook runner resolves '' to the default at execution
@@ -238,6 +252,7 @@ export function getSettings(ctx: ExtensionContext): Settings {
     reviewPrompt,
     devBranch,
     autoBuildBranch,
+    worktreeDirectory,
     worktreePostCreateScript,
     worktreePreRemoveScript,
     implTabPreCreateScript,