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

Cargo.lock

@@ -3369,6 +3369,7 @@ checksum = "20870f649af7073d53e38067b2a84312175d56ea15217e1b15bc83506ec50afb"
 name = "ledger-cli"
 version = "0.1.0"
 dependencies = [
+ "serde_json",
  "tempfile",
  "toml 1.1.8+spec-1.1.0",
 ]