fix(bridge): confirm before wiping non-empty convert output dir

[glours]

What I did
bridge convert -o <dir> unconditionally ran os.RemoveAll on the output directory and discarded any error, so a typo (-o ., -o $PWD, -o ~) silently destroyed unrelated user data.

An empty or missing output directory is still created silently, but a non-empty one now requires explicit confirmation (prompted interactively, or via the new --yes flag for scripts/CI) before being wiped.

Related issue
https://docker.atlassian.net/browse/DDB-683

(not mandatory) A picture of a cute animal, if possible in relation to what you did

[docker-agent]

Assessment: 🟢 APPROVE

The safety guard is correctly implemented. prepareOutputDir checks for a non-empty directory, prompts for confirmation (or auto-confirms via --yes), and only then calls os.RemoveAll + os.MkdirAll — all with proper error propagation. The --yes flag is wired correctly through the CLI layer. The new FileAbsent / FileContains check helpers and the two Scenario-based e2e tests cover both the confirmed and declined paths cleanly.

Two hypotheses were raised and investigated during review:

• Non-TTY stdin behaviour without --yes: NewPrompt already branches on stdin.IsTerminal() and returns a Pipe implementation for non-TTY contexts. Pipe.Confirm reads via fmt.Fscanln; on EOF it silently gets an empty string, StringToBool("") → false, and the convert is declined with an explicit error — no hang, no silent data destruction. ✅ Dismissed.
• E2E declined-path test hanging: The test intentionally exercises the non-TTY decline path. Because Pipe.Confirm returns false on EOF stdin, the command exits with code 1 and the guard file is untouched — exactly what ExitCode(1) + FileContains assert. ✅ Dismissed.

[codecov]

Codecov Report

❌ Patch coverage is 70.45455% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/bridge/convert.go	63.88%	9 Missing and 4 partials ⚠️

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