Fix ambiguous explain-flag test assertion and build failure in interactive mode

[Copilot]

TestRunWithExplainTrue asserted on "explain-test", which also appeared in the command's own output (echo explain-test), making the test vacuously pass even with broken explanation logic. Additionally, fatih/color's Printf writes to a package-level Output captured at init time, bypassing os.Stdout redirects in tests entirely.

Changes

• internal/executor/executor.go: Switch dimColor.Printf(...) → dimColor.Fprintf(os.Stdout, ...) so explanation output goes to the current os.Stdout, making it capturable via pipe redirect in tests.

• internal/executor/executor_test.go: Use a command (echo hello) whose output cannot overlap with the explanation, and assert on a unique explanationText constant:

  const explanationText = "Unique explanation string that only appears in the explanation output."
  // ...
  if !strings.Contains(output, explanationText) { ... }

• internal/config/config.go: Add Explain bool \toml:"-"`toConfig— runtime-only, not persisted — to resolve the build failure whererepl.goreferencedcfg.Explain` without the field existing.

• cmd/root.go: Set cfg.Explain = explainFlag before entering interactive mode so the flag propagates through the REPL path.

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[Copilot]

Pull request overview

This PR fixes a vacuously-passing --explain test and resolves an interactive-mode build failure by ensuring explanation output is capturable via os.Stdout redirection and by plumbing the explain flag through interactive configuration.

Changes:

• Make executor explanation output write to the current os.Stdout so tests can capture it.
• Strengthen TestRunWithExplainTrue by using a non-overlapping command output and asserting on a unique explanation string.
• Add a runtime-only Config.Explain field and propagate --explain into interactive mode.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/executor/executor.go	Sends explanation output to os.Stdout (capturable in tests / redirectable).
internal/executor/executor_test.go	Removes ambiguous assertion by using unique explanation text and echo hello.
internal/config/config.go	Adds Config.Explain as a non-persisted runtime flag carrier.
cmd/root.go	Sets cfg.Explain before entering interactive mode so REPL execution respects --explain.

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