fix: exit non-zero when a file cannot be processed

[MPV]

What

Make kir fail loud via the exit code instead of silently reporting success. Two related fixes (the second folded in from #57):

1. A file that can't be processed → non-zero exit. Per-file errors were logged but Run still returned 0.
2. An argument that matches nothing → error + non-zero exit. filepath.Glob returns no matches and no error for both an empty glob and a missing literal path, so a typo was silently skipped.

Before → After

$ kir good.yaml broken.yaml; echo "exit=$?"
# before: prints good image, logs error, exit=0   ← success despite the error
# after:  prints good image, logs error, exit=1

$ kir typo.yaml; echo "exit=$?"
# before: (no output) exit=0                        ← typo silently ignored
# after:  error: no such file or match for "typo.yaml"  exit=1

Successes are still printed either way — kir is best-effort and never aborts the batch on one bad input; only the exit status changes.

Why

For a tool feeding a scanner (kir manifests/* | xargs grype), a zero exit must mean every input was understood. A parse failure or a mistyped path silently exiting 0 is the dangerous gap.

Tests

• TestFailure/BadYAML (approval): malformed manifest through cmd.Run → error on stderr + exit 1 (exits 0 without this change).
• TestCLI.MissingFile (approval): no-match argument → error + exit 1.
• cmd_test.go TestRunFileFailure and fileutil unit tests cover the same at their layers.

Docs

Records the contract as docs/adr/0008-best-effort-processing-and-exit-codes.md (best-effort; failures surface via the exit code) and points ADR 0007's exit-column reference at it.

Release

Based on master. fix: → patch. (Combines the former #55 + #57, which is merged into this branch.)

🤖 Generated with Claude Code

https://claude.ai/code/session_01Pc6NAURAqjU4LYJx93tgSC