Viewer: click a vault TIN to copy the full number

The party page's "TIN on file" and the W-9 card's TIN copy the full,
formatted number on click (right-click: digits only). The viewer reads
it from the vault only at that moment, with the server's key file in
force, never creates a key, refuses a key inside the books dir, and
never draws more than the last four. A locked vault copies nothing and
says why.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GWVo7x3UHw5kwCUaWxiejX

crates/ledger-gui/Cargo.toml

@@ -15,6 +15,7 @@ ledger-core = { path = "../ledger-core" }
 ledger-store = { path = "../ledger-store" }
 ledger-config = { path = "../ledger-config" }
 ledger-import = { path = "../ledger-import" }
+ledger-vault = { path = "../ledger-vault" }
 eframe = { version = "0.36", default-features = false, features = ["default_fonts", "wgpu", "wayland", "x11", "persistence"] }
 egui = "0.36"
 egui_extras = { version = "0.36", features = ["image", "datepicker", "serde"] }