P2 slice 5: files in and out

Files reach the books through the server: uploads by hash and size,
then filed; exports (the CPA package, the 1099 worksheet, W-9s) handed
over as downloads from the server, never read off disk by the agent.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T3gXMVt7XJPi6ens1or9Dj

crates/ledger-host/src/tokens.rs

@@ -27,7 +27,7 @@ use std::path::{Path, PathBuf};
 /// The keyring service tokens are kept under (INVARIANT 1).
 pub const SERVICE: &str = "wanderbooks";
 /// A token's name when none is given.
-pub const DEFAULT_NAME: &str = "agent";
+pub const DEFAULT_NAME: &str = ledger_store::auth::DEFAULT_NAME;
 
 /// A place tokens are kept.
 pub trait Keeper: Send + Sync {