fix(cli): exit non-zero on red error paths

[usmamalik345]

Summary

• CLI red-error handlers that previously printed and returned (exit 0) now raise SystemExit(1), matching the house idiom in review.py.
• Covered the handlers listed in fix(cli): error handlers across nine files print and return, leaving exit code 0 #164 (return-paths and fall-offs).
• Left alone: yellow "reindex already running" (HTTP 409) — informational, not a hard failure.
• Added regression tests patterned on tests/test_cli_stop.py.

Fixes #164

Test plan

• pytest tests/test_cli_error_exit_codes.py tests/test_cli_stop.py (17 passed)
• Spot-check: force an API failure on palinode depends --unblocked / palinode trace … and confirm non-zero exit

Assisted-by: Cursor

[Paul-Kyle]

Complete, and the part I want to call out is the 409. The issue said that sweep was a floor rather than a proof and asked you to judge each site — you left "reindex already running" at exit 0, pinned it with a test, and said why in both the issue and the PR instead of leaving it to be found in the diff. That is the whole reason it was help wanted and not a first issue.

Also right, and easy to get wrong: the raise in depends.py is inside the except rather than at the return below it, which would have caught the success path too. And you left the ten bare click.Abort() calls alone — those are #162's, and staying out of them keeps whoever takes it from rebasing.

Merging. Thanks for a strong first contribution.