Stamp Docker image version from the host; flush profiles on error exit (closes #75)

Docker images reported commit unknown because the build ran git inside the container while .dockerignore excludes .git, and VERSION was never overridden. script/docker and script/cibuild now compute version, commit and date on the host and pass them as build args; the Dockerfile runs no git and falls back to dev and unknown, never empty, on a bare docker build.

Profiling a failing command gave a truncated or missing profile: Entry and each command goroutine called os.Exit(1), skipping the deferred profile writers in main. Entry now returns a status that main exits with after its defers run, and command goroutines report failure through one RunOperation helper, which also restores PID-lock release and graceful shutdown on failure.

model: claude-opus-4-8 (implementation, review); claude-fable-5-1 (merge)

Co-authored-by: clawbot <clawbot@noreply.example.org>

internal/cli/entry_banner_test.go

@@ -230,7 +230,7 @@ func TestEntryJSONStdoutIsExactlyOneDocument(t *testing.T) {
 		programName, flagConfig, configPath, cmdSnapshot, cmdList, flagJSON,
 	}
 
-	stdout := captureProcessStdout(t, Entry)
+	stdout := captureProcessStdout(t, func() { _ = Entry() })
 
 	requireExactlyOneJSONDocument(t, stdout)