feat(editor): Implemented / overridden gutter markers (#106)

Adds gutter markers for type hierarchies: ↓ "Is implemented / Has subclasses / Is overridden" on types and methods with implementations, ↑ "Implements / Overrides method in X" on methods that implement or override a supertype method. One target navigates, several open the Choose Implementation popup. Settings › Editor › General › Gutter Icons gets two toggles.

Markers come from the language server: a new batched `lsp_implementations` command (up to 4 concurrent, cancellable, sharing the goto query path) for ↓, and the Super Method lookup for ↑, which now prefers the overload with matching parameters (also fixes ⌘U on overloads). Only declarations near the viewport are queried, debounced, cached per document version and cancelled when superseded. Works for any server with implementation / type hierarchy support; servers without type hierarchy show ↓ only.

Fixes #99

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

src/platform/locales/text/zh.json

@@ -3708,6 +3708,20 @@
   "Can't rename '{name}' without the language server: only local variables can be renamed based on syntax": "没有语言服务器时无法重命名 '{name}'：基于语法只能重命名局部变量",
   "Choose Super Class or Interface ({count} found)": "选择超类或接口（找到 {count} 个）",
   "Choose Super Method of {name} ({count} found)": "选择 {name} 的超方法（找到 {count} 个）",
+  "Choose Implementation of {name} ({count} found)": "选择 {name} 的实现（找到 {count} 个）",
+  "Choose Subclass of {name} ({count} found)": "选择 {name} 的子类（找到 {count} 个）",
+  "Choose Overriding Method of {name} ({count} found)": "选择 {name} 的重写方法（找到 {count} 个）",
+  "Is implemented by {names}": "由 {names} 实现",
+  "Is subclassed by {names}": "子类：{names}",
+  "Is implemented in {names}": "在 {names} 中实现",
+  "Is overridden in {names}": "在 {names} 中重写",
+  "Implements method in {names}": "实现 {names} 中的方法",
+  "Overrides method in {names}": "重写 {names} 中的方法",
+  "{names} and {count} more": "{names} 等另外 {count} 个",
+  "Implemented and overridden": "已实现和已重写",
+  "Implementing and overriding": "实现和重写",
+  "Implemented and overridden declarations": "已被实现和重写的声明",
+  "Implementing and overriding methods": "实现和重写超类型方法的方法",
   "Replace all {count} occurrences": "替换全部 {count} 处",
   "↵ Apply · Esc Keep '{name}'": "↵ 应用 · Esc 保留 '{name}'",
   " (in {files} files)": "（位于 {files} 个文件中）",