[fzlzjerry]

Addresses #1060 and the configuration/default interaction discussed in #544.

NO_COLOR is already supported, but the environment check treats an empty value as active and ignores non-Unicode values on Unix. Explicit color.when: always also loses to the environment, contrary to the configuration override guidance.

This change:

• Reads NO_COLOR as an OS string and only treats nonempty values as active.
• Lets explicit always/never color configuration override the environment. auto, including the built-in default, still honors NO_COLOR, so the default configuration does not accidentally turn the variable off.
• Preserves command-line overrides and classic-mode behavior. Theme definitions and the generic precedence for other flags are unchanged.
• Adds unit/CLI coverage and documents the behavior in the README, man page and config samples.

Validation on Linux:

• Full Cargo-built test binaries pass with Rust 1.85.0 and 1.98.0, default and no-default features, with NO_COLOR both unset and set. Each default run has 443 tests; each no-default run has 439. Runs use non-root private namespaces, including the permission-sensitive tests.
• Four color unit cases and the new CLI regression fail on the original implementation and pass with the change.
• 17 real pseudo-terminal cases pass for each of the four version/feature binaries, covering empty/nonempty/non-Unicode values, no user config, explicit config and CLI overrides.
• The CI-pinned Rust 1.85.0 passes formatting, cargo clippy --locked --tests -- -D warnings and the clap/deprecated check. Rust 1.98.0's stricter Clippy reports the same 10 existing diagnostics on the clean base and this patch, all in unchanged files; its formatting and clap/deprecated check pass.
• The man page builds with the project's Pandoc command. Dependencies and the lockfile are unchanged.

---

TODO

• Use cargo fmt
• Add necessary tests
• Update README
• Update config sample file in doc/samples
• Update man page at doc/lsd.md

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