feat(db): 待处理新增「下载器连不上」「下载目录读不到容量」两类（迁移 0073）

decision.kind 增加 downloader_offline / cache_volume_unknown,契约、原因文案与界面标签同步;
volume_state_unknown 的原因文案改为「下载目录读不到容量」并指向路径映射与容器挂载。

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

packages/db/src/types.ts

@@ -112,7 +112,9 @@ export type DecisionKind =
   | "source_unreachable"
   | "other"
   | "identity_unresolved"
-  | "episode_mapping";
+  | "episode_mapping"
+  | "downloader_offline"
+  | "cache_volume_unknown";
 export type DecisionStatus = "open" | "investigating" | "awaiting_user" | "resolved" | "dismissed" | "expired";
 export type DecisionSeverity = "info" | "warning" | "critical";
 export type DownloadTaskOrigin = "submitted" | "adopted";