fix(web): visual QA front-end items U4–U6, U13–U16 and copy list

- U4: form save failures toast the first problem and scroll/focus the first
  invalid field (policy draft, settings cards, resource drawers, subscription
  form) via lib/form-errors.
- U5: FormField keeps 8px between a hint and the next label.
- U6: file manager status bar keeps free space left-aligned, clear of the
  Agent button.
- U13: move/copy dialog stops "target is the source folder / inside the
  source" before requesting a preview (transferTargetProblem + tests).
- U14: account popover uses the solid float material.
- U15/U16: inbox tile hint shortened; TMDB assign dialog uses the shared
  Select and labelled fields (type, TMDB ID, note).
- Copy: "TMDB 已保存" spacing, API Key block no longer repeats the section
  title, whole-day intervals read "每 7 天", "最高级别:提示",
  "延后:已有计划在途", failed records show "未生成目标路径", upstream model
  column "默认模型".

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/files/dialogs.tsx

@@ -55,6 +55,7 @@ import {
   newIdempotencyKey,
   splitCommon,
   stemRange,
+  transferTargetProblem,
 } from "./model.ts";
 
 // ─── 共用 ───────────────────────────────────────────────────────
@@ -485,6 +486,11 @@ export function TransferDialog({
   const runPreview = (t: FileRef, m: "move" | "copy") => {
     setPlan(null);
     setErr(null);
+    const problem = transferTargetProblem(items, t);
+    if (problem) {
+      setErr(problem);
+      return;
+    }
     dry.mutate(
       { idempotencyKey: `${key}-dry-${m}-${t.root}-${t.path}`, items, target: t, mode: m, dryRun: true },
       { onSuccess: setPlan, onError: (e) => setErr(filesErrorText(e, "预览失败")) },