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/routes/console/files.tsx

@@ -1088,7 +1088,8 @@ export default function FilesPage() {
                   {totalSize(selected) ? ` · ${formatBytes(totalSize(selected), 1)}` : ""}
                 </span>
               ) : null}
-              {root.usage ? <span className="ml-auto">剩余 {formatBytes(root.usage.freeBytes, 1)}</span> : null}
+              {/* 靠左排:右下角是 Agent 悬浮按钮(QA U6) */}
+              {root.usage ? <span>剩余 {formatBytes(root.usage.freeBytes, 1)}</span> : null}
               {!root.writable && root.kind === "library" ? <StatusBadge>只读</StatusBadge> : null}
             </div>
           ) : null}