test(cli): verify dotenv export round trips

[Akimbo92i]

Summary

Add regression coverage proving that Sotto can parse its own dotenv export without changing names, values, or entry order.

Changes

• Add a table-driven dotenv render-and-parse round-trip test.
• Cover empty input and representative values including whitespace, quotes, backslashes, control characters, literal escape text, $, #, =, and non-ASCII UTF-8.
• Compare the complete ordered entry vector with the original input.

Testing

• cargo test -p sotto-cli export::tests
• cargo fmt --all --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

The repository script suite was also attempted during independent review. Eight cargo-audit fixture tests could not generate temporary lockfiles from the offline dependency cache; this contribution changes neither manifests nor Cargo.lock.

Related Issue

Closes #187

[github-actions]

Thanks for your first pull request to Sotto, and welcome.

Two things that trip up newcomers:

• Every commit needs a Signed-off-by line under the Developer Certificate of Origin - PRs with unsigned commits cannot be merged. Sign off with git commit -s; if your branch already has unsigned commits, run git rebase --signoff main and push again.
• Please run cargo fmt --all --check and cargo clippy --workspace --all-targets -- -D warnings before pushing, and add tests for new behaviour (cargo test --workspace runs the suite).

The full guide is in CONTRIBUTING.md - a maintainer will review shortly.

[Maxerns]

Thanks @Akimbo92i this matches the issue exactly: all the required cases are there, real control characters are correctly distinct from their literal spellings, and the full vector assertion is the right check. Test only scope, signed off, and thanks for flagging the unrelated audit fixture noise in your environment.

One follow up on that: the audit suite is green on CI and locally here, so it looks environment-specific could you paste the error output? If it shows a real portability gap I'll file it as a separate issue.

Approving CI now; once it's green I'll merge.