ImageDescriber exits 0 on every failure (Ollama unreachable, missing import file, missing required option, failed images) #167

What's wrong

In ImageDescriber/Program.cs (~lines 22–28), Main returns void, and Parser.Default.ParseArguments(...).WithParsed(...) ignores parse errors. Each verb's Run reports a failure with Console.WriteLine and then returns normally.

Reproduced, and each of these exits with 0:

Why it matters

A script, CI job or scheduled task that runs ImageDescriber Scan cannot tell that nothing, or only part of the folder, was described. OAICLI recently fixed the same problem in commit 5ecfd8e ("exit non-zero when the OpenAI API rejects a request").

Suggested fix

• Make Main return int, and map WithNotParsed to 1.
• Have BaseVerb.Run return a status (or set Environment.ExitCode) so that failures are non-zero: Ollama unavailable, missing or wrong input file, unwritable output, and a non-empty scan failure list.

Acceptance criteria

• Each command in the table above exits non-zero.
• Successful runs still exit 0.
• A test asserts the exit status for at least the parse-error and Ollama-unavailable cases.