node-lookup: auto-qualify short node names to .main.unkin.net (#19)

Short `-n` node names silently returned nothing: `node-lookup -R -n ausyd1nxvm2120` found nothing while `-n ausyd1nxvm2120.main.unkin.net` worked, because the PuppetDB `certname` filter needs a FQDN. This auto-qualifies a dotless name before the lookup.

## Changes
- Add `qualifyNode()` pure helper: a dotless name gets `.<domain>` appended; a name already containing a dot (any domain, incl. `*.k8s.syd1.au.unkin.net`) is left unchanged; a single trailing dot is stripped first; empty input is preserved (same "no node" behavior as today).
- Apply normalization to the `-n` value and to stdin-sourced node names in `run()`, so both entry points behave consistently.
- Make the domain configurable: config key `domain`, `NODE_LOOKUP_DOMAIN` env var, and `--domain` flag, all defaulting to `main.unkin.net`.
- Surface `domain` in `config show` / `config init` output and document the new env var/flag/behavior in AGENTS.md.
- Add table-driven `qualifyNode` tests (short name appended, FQDN unchanged, multi-label other-domain FQDN unchanged, trailing-dot handling, empty input, custom domain) and a `NODE_LOOKUP_DOMAIN` env-override test.

Companion tools `pburl`/`pblastreport` take already-qualified hostnames (typically piped from `node-lookup`) via `puppet.ReadHosts` and do not share the `-n` code path, so they are intentionally left out to keep this PR atomic.

## Validation
- `gofmt -l .` clean, `go vet ./...` clean
- `go test -race ./...` pass
- `make build` builds all three binaries

Reviewed-on: #19
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

AGENTS.md

@@ -138,10 +138,12 @@ Show the active configuration (after all overrides applied):
 | `NODE_LOOKUP_URL` | `puppetdb_url` | PuppetDB facts endpoint |
 | `NODE_LOOKUP_ROLE_FACT` | `role_fact` | Fact name used by `-R` flag |
 | `NODE_LOOKUP_PUPPETBOARD_URL` | `puppetboard_url` | Puppetboard base URL (pburl / pblastreport) |
+| `NODE_LOOKUP_DOMAIN` | `domain` | Domain appended to short (dotless) `-n` node names (default `main.unkin.net`) |
 
-### CLI flag
+### CLI flags
 
 `--url <url>` overrides the PuppetDB URL for a single invocation (highest precedence).
+`--domain <domain>` overrides the auto-qualify domain for a single invocation.
 
 ## Code Patterns
 
@@ -152,6 +154,7 @@ Show the active configuration (after all overrides applied):
 - **`queryPuppetDB(url, query)`**: takes the URL as a parameter — never reads globals.
 - **`processResults()`**: iterates facts, returns sorted `"certname value"` strings. JSON string values are unquoted; other JSON types rendered as compact JSON.
 - **Output modes**: JSON (`-j`), count (`-C`), Ansible YAML (`-A`), node-only (`-1`), value-only (`-2`), default (node + value). `-j` and `-A` share `factsByHost()`, so both attach the queried fact(s) per host — as an object under the host (`-j`) or as inventory host vars (`-A`).
+- **Short node names / `qualifyNode()`**: a `-n` value (and stdin-sourced node names) with no dot is auto-qualified to `<name>.<domain>` (domain defaults to `main.unkin.net`, overridable via `--domain`/`NODE_LOOKUP_DOMAIN`), so `-n ausyd1nxvm2120` resolves the same as its FQDN. A name that already contains a dot (any domain) is left unchanged; a single trailing dot is stripped; empty input is preserved.
 - **Stdin support**: `stdinReader()` reads node names from stdin only when it is a real pipe/redirect carrying data (and no `-n` given). Terminals, `/dev/null`, and empty/closed pipes fall through to a normal query — so running without a TTY (e.g. invoked by an agent or CI) behaves like an interactive run instead of consuming empty input.
 - **SIGPIPE handling**: `signal.Ignore(syscall.SIGPIPE)` so pipes to `head` etc. work cleanly.