Extract command state from App

[garritfra]

Summary

• Add CommandState for command prompt line, kind, history, history index, and scratch state.
• Route command editing, submit bookkeeping, and history navigation through CommandState helpers.
• Update render, search, dispatch, and mouse test call sites to use the grouped command state.

Test plan

• cargo fmt --all
• cargo clippy --workspace --all-targets --all-features
• cargo test

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