feat: one-command onboarding — wanderbooks new, install.sh, justfile

wanderbooks new DIR installs the server and GUI if missing, writes the
books dir (AGENTS.md + CLAUDE.md, wanderbooks.toml, justfile, .mcp.json,
.claude/settings.json approving the server), commits, and starts claude
onboarding. install.sh: Rust + cargo install + wanderbooks new in one
line. The tax summary labels its net when accounts are uncategorized.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MtYEaR6M6Ybdhm6X98BWNu

crates/ledger-cli/Cargo.toml

@@ -4,13 +4,14 @@ version = "0.1.0"
 edition.workspace = true
 license.workspace = true
 repository.workspace = true
-description = "wanderbooks CLI: scaffold new books directories (mise.toml + AGENT.md)."
+description = "wanderbooks CLI: one command from nothing to a working books directory."
 
 [[bin]]
 name = "wanderbooks"
 path = "src/main.rs"
 
 [dev-dependencies]
+serde_json = "1"
 toml = "1"
 tempfile = "3"