fix: set binary name to arborist instead of arborist-cli

[montfort]

Summary

• Add [[bin]] name = "arborist" to Cargo.toml so the installed binary is arborist, not arborist-cli
• Update self_update bin_name to match
• Update all test references from cargo_bin("arborist-cli") to cargo_bin("arborist")
• Bump version to 0.1.1

Test plan

• cargo test — 29 tests pass
• arborist --version prints arborist 0.1.1
• cargo fmt --check and cargo clippy pass

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