Package as RPM, add completions, fix no-TTY behavior, repair tests

The test suite no longer compiled after the -p/-i match-modifier refactor,
there was no RPM packaging or shell-completion story, and running without a
TTY against an empty pipe silently returned nothing.

- Replace the fragile !isTerminal stdin check with stdinReader(): only read
  node names when stdin is a real pipe/redirect carrying data, so /dev/null,
  terminals, and empty/closed pipes fall through to a normal query (works when
  invoked by an agent/CI with no TTY).
- Rewrite main_test.go to match the current buildQuery/run signatures and add
  coverage for match modifiers, output modes, config precedence, and the new
  stdinReader logic.
- Add nfpm packaging (packaging/nfpm.yaml, scripts/build-rpm.sh) that installs
  the binary to /usr/bin and bundles generated bash/zsh/fish completions.
- Rework the Makefile to build into dist/ and add completions/rpm targets.
- Split the PR CI into build + test + pre-commit workflows and extend release
  to build the RPM and PUT it to the artifactapi rpm-internal repo; every step
  now sets a serviceAccount and k8s resources.

.woodpecker/build.yaml

@@ -0,0 +1,18 @@
+when:
+  - event: pull_request
+
+steps:
+  - name: build
+    image: golang:1.25
+    commands:
+      - make build
+    backend_options:
+      kubernetes:
+        serviceAccountName: default
+        resources:
+          requests:
+            memory: 512Mi
+            cpu: 1
+          limits:
+            memory: 2Gi
+            cpu: 2