fix(downloads): humanized reasons and TechInfo on the download panel (DL-2b)

- board organize hint uses DEAI-2 reasonLine; add transfer_failed, blocked,
  blocked_by_conflict, main_failed, not_imported_kind, target_root_not_managed,
  download_removed to the reason table with tests
- download detail / plans tab: internal ids, raw codes and JSON moved into TechInfo
- library versions tech block switched to TechInfo (TODO(DEAI-2))
- copy: glossary terms (no 接管/候选), plan reason codes no longer shown raw

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

apps/web/app/api/tasks.ts

@@ -191,7 +191,7 @@ export function buildTimeline(input: {
     key: "dl-submit",
     stage: "download",
     at: task.createdAt,
-    title: task.origin === "adopted" ? "接管已有下载" : "提交下载",
+    title: task.origin === "adopted" ? "开始管理已有下载" : "提交下载",
     detail: task.name,
     tone: "neutral",
   });
@@ -230,7 +230,7 @@ export function buildTimeline(input: {
       stage: "download",
       at: task.updatedAt,
       title: "下载器报错",
-      detail: String((task.lastError as { message?: unknown }).message ?? JSON.stringify(task.lastError)),
+      detail: humanizeReason(String((task.lastError as { message?: unknown }).message ?? "")) || null,
       tone: "destructive",
     });
   for (const r of records) {