vault: files sealed under a password that is never stored

Argon2id turns the vault password into a key that seals a random master
key; only the sealed copy is kept. Each file gets its own key, sealed
under the master key in its header with its media id, and its bytes are
AES-256-GCM STREAM records, so a swapped, cut or altered file refuses
to open. Uploads with ?encrypt=true are sealed as they stream in.

:vault, :unlock, :lock, :passwd, :encrypt, :decrypt and :upload! drive
it. The vault locks after WORKSPACE_VAULT_IDLE_MIN idle minutes, on
logout and on restart; while locked, sealed files answer 423, share
links never serve them, and :export! refuses rather than leave them out.

Sealing an existing file rewrites it under a new id and retires the old
one: the mirror deletes the plaintext from Proton Drive outright,
trash included, whatever WORKSPACE_BACKUP_PRUNE says, and drops it from
the readable files/ view. The mirror now compares on-disk sizes, so
sealed files are not re-hashed every run.

src/routes/mod.rs

@@ -4,9 +4,11 @@ pub mod nodes;
 pub mod export;
 pub mod import;
 pub mod media;
+pub mod seal;
 pub mod session;
 pub mod share;
 pub mod ssh_keys;
+pub mod vault;
 
 use axum::{
     routing::{delete, get, post, put},
@@ -39,6 +41,11 @@ pub fn api_router() -> Router<AppState> {
         .route("/nodes/{id}/move", post(nodes::move_node))
         .route("/nodes/{id}/import", post(import::import))
         .route("/nodes/{id}/files", post(media::upload_into))
+        .route("/nodes/{id}/encrypt", post(seal::encrypt))
+        .route("/nodes/{id}/decrypt", post(seal::decrypt))
+        .route("/vault", get(vault::status).post(vault::setup).put(vault::change_password))
+        .route("/vault/unlock", post(vault::unlock))
+        .route("/vault/lock", post(vault::lock))
         .route("/nodes/{id}/share", post(share::enable))
         .route("/nodes/{id}/share", delete(share::disable))
         .route("/media", post(media::upload).get(media::list))