[codex] refactor for antislopus linter

[alexfedosov]

Summary

Refactors the Go codebase so the antislopus comprehension linter reports zero findings.

• Splits the large TUI model and view implementations into focused package files.
• Flattens branch-heavy parsing, clipboard, git, syntax, autocomplete, rendering, and update logic.
• Restructures tests with focused helpers so test bodies stay shallow while preserving coverage.

Impact

This is intended to preserve behavior while improving scanability and keeping the project compliant with the updated linter rules.

Validation

• find . -name '*.go' -not -path './.git/*' -print0 | xargs -0 gofmt -l
• go test ./...
• cargo run --manifest-path ../antislopus/Cargo.toml -- .