fix(canvas): 提示词编辑 - 修复小视口溢出与窗口调整手柄失效

Refs #507

web/src/lib/canvas/canvas-prompt-editor-size.ts

@@ -0,0 +1,12 @@
+type Size = { width: number; height: number };
+
+export const PROMPT_EDITOR_VIEWPORT_MARGIN = 24;
+
+export function clampPromptEditorModalSize(size: Size, viewport: Size): Size {
+    const maxWidth = Math.max(1, viewport.width - PROMPT_EDITOR_VIEWPORT_MARGIN);
+    const maxHeight = Math.max(1, viewport.height - PROMPT_EDITOR_VIEWPORT_MARGIN);
+    return {
+        width: Math.min(maxWidth, Math.max(560, Math.round(size.width))),
+        height: Math.min(maxHeight, Math.max(320, Math.round(size.height))),
+    };
+}