test: stub Range layout methods once in the test setup (#53)

Root cause: jsdom has no layout and CodeMirror measures text ranges in an animation frame, sometimes after a test finished; test files that did not stub Range.getClientRects (e.g. search/codePreview) threw an unhandled TypeError that failed whole CI runs at random (seen on #41).
Fix: stub Range.getClientRects / getBoundingClientRect once in src/test/setup.ts; drop the six per-file copies.
Verified: vitest on editor/lsp, editor/refactor, templates, search (55 files, 458 tests, no unhandled errors).

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

src/editor/refactor/introduce.test.ts

@@ -120,10 +120,6 @@ const { clearLevelCache } = await import("./projectLevel");
 
 // --- editor ---------------------------------------------------------------------
 
-// jsdom has no layout; popups anchor at caret coordinates.
-Range.prototype.getClientRects ??= () => [] as unknown as DOMRectList;
-Range.prototype.getBoundingClientRect ??= () => new DOMRect();
-
 let view: EditorView | null = null;
 
 function editor(doc: string, language: string, path: string, sel: { anchor: number; head?: number }) {

src/editor/refactor/refactorThis.test.ts

@@ -55,10 +55,6 @@ const { lspDoc } = await import("@/editor/lsp/lsp");
 const { inplaceRenameExtension, inplaceSession } = await import("@/editor/lsp/inplaceRename");
 const { temporaryHighlights } = await import("@/editor/lsp/tempHighlight");
 
-// jsdom has no layout; popups anchor at the caret.
-Range.prototype.getClientRects ??= () => [] as unknown as DOMRectList;
-Range.prototype.getBoundingClientRect ??= () => new DOMRect();
-
 const action = (title: string, kind: string, disabledReason: string | null = null): CodeAction => ({
   title,
   kind,