vault: a sealed folder stays sealed

`:encrypt` on a folder sealed the files in it once; whatever arrived
afterwards was plaintext. A folder or space that is encrypted now
carries `sealed` (0015), and so does every folder under it, so "is
this place sealed?" is one column of the parent. What lands there is
sealed on the way in, or refused with 423 while the vault is shut:

- uploads, with or without `?encrypt`, encrypted as they stream
- imports, sealed where they lie before any row names them
- SFTP writes, sealed out of their `.part`, and refused at the open
  when the vault is shut
- files and folders moved in, through the web or SFTP: seal::enter
  seals them first and the move happens only if that worked

Triggers make it hold for any path: a folder made inside a sealed one
is sealed, and a file node whose media is not encrypted cannot be
inserted into or moved into a sealed folder (a 400, not a 500).
Decrypting the sealed folder lifts the flag on its subtree and opens
its files; a file or folder inside it cannot be decrypted on its own.
An empty folder can be sealed. Documents are not files and stay as
they are.

The list shows a lock on sealed folders, the touch menu offers to
unseal one, and an upload or import into one asks for the vault
password first. Tests cover sealing, inheritance, the trigger, moves
with the vault open and shut, unsealing, an SFTP write and an import.

web/src/lib/api.ts

@@ -30,6 +30,8 @@ export interface NodeSummary {
   updated_at: number
   shared: boolean
   share_token: string | null
+  /** Folders and spaces only: whatever lands here is sealed in the vault. */
+  sealed: boolean
   /** Files only. */
   file: FileInfo | null
   /** Search results only: where the match sits, `work/notes`. */
@@ -433,9 +435,12 @@ export const api = {
 
   lockVault: () => request<VaultStatus>('/vault/lock', { method: 'POST' }),
 
-  /** Seal a file, or every file under a folder, into the vault — or take it back out. */
+  /**
+   * Seal a file into the vault, or a folder with everything in it and all
+   * that lands there later — or take it back out.
+   */
   seal: (id: number, encrypt: boolean) =>
-    request<{ files: number; unchanged: number; failed: number; shared: number }>(`/nodes/${id}/${encrypt ? 'encrypt' : 'decrypt'}`, {
+    request<{ files: number; unchanged: number; failed: number; shared: number; sealed: boolean }>(`/nodes/${id}/${encrypt ? 'encrypt' : 'decrypt'}`, {
       method: 'POST',
     }),