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-cli/Cargo.toml

@@ -23,6 +23,7 @@ ledger-store = { path = "../ledger-store" }
 ledger-gui = { path = "../ledger-gui", optional = true }
 
 [dev-dependencies]
+base64 = "0.22"
 chrono = "0.4"
 libc = "0.2"
 reqwest = "0.13"
@@ -32,6 +33,7 @@ ledger-config = { path = "../ledger-config" }
 ledger-core = { path = "../ledger-core" }
 ledger-vault = { path = "../ledger-vault" }
 serde_json = "1"
+sha2 = "0.10"
 toml = "1"
 tempfile = "3"