feat(config): support ordered key-binding behaviors #44

Parent

Part of #43.

Summary

Extend [key-bindings] so each OS can define a chord and an ordered behavior chain.

[key-bindings]
macos = { key = "ctrl-o", behaviors = ["zoxide", "cj"] }
linux = { key = "alt-o", behaviors = ["cj", "zoxide"] }
windows = { key = "ctrl-o", behaviors = ["cj"] }

An empty behaviors array disables the binding. Preserve the existing string form as a shorthand for the default behavior chain where practical.

Semantics

• evaluate behaviors from left to right
• zoxide and cj are the initial allowed values
• unavailable dependencies or an empty candidate source advance to the next behavior
• user cancellation stops evaluation without modifying the buffer or directory
• an actual execution error stops evaluation and produces a durable shell-visible diagnostic
• do not add an implicit dependency-based auto mode
• reject unknown, duplicate, or invalid behavior entries with actionable configuration errors

Acceptance criteria

• parsing, validation, defaults, serialization, and sample configuration cover the new structure
• the selected OS binding is deterministic
• an empty chain renders no key binding
• generated shell integration receives the ordered configuration without re-reading TOML on every keypress
• tests cover both behavior orders, single-behavior configurations, disabled bindings, shorthand migration, and invalid values

Delivery

Implemented in #53 and released in 0.4.0 as part of #43.