Re-vendor the shared files from sneak/prompts at dd4027b (closes #52)

Takes .golangci.yml, .dockerignore, .gitignore, .editorconfig, the
workflow and REPO_POLICIES.md from sneak/prompts dd4027b, keeping this
repository's own entries after the shared content. Lint (golangci-lint
v2.14.0) and test become Dockerfile phases that script/lint and
script/test build alone and uncached; the image build depends on both,
and script/cibuild bootstraps, runs script/check, then builds the image.
The agent guidance file moves to AGENTS.md. The Go code is fixed for
what the new configuration finds; reads that iterate rows now also
report an iteration error.

Model: opus-5-5

cmd/asinfo-gen/main.go

@@ -2,8 +2,10 @@
 package main
 
 import (
+	"context"
 	"encoding/csv"
 	"encoding/json"
+	"errors"
 	"io"
 	"log"
 	"net/http"
@@ -27,13 +29,17 @@ func main() {
 
 	// Fetch the CSV data
 	log.Println("Fetching AS CSV data...")
-	resp, err := http.Get(asCsvURL)
+
+	req, err := http.NewRequestWithContext(
+		context.Background(), http.MethodGet, asCsvURL, nil)
+	if err != nil {
+		log.Fatalf("Failed to fetch CSV: %v", err)
+	}
+
+	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		log.Fatalf("Failed to fetch CSV: %v", err)
 	}
-	defer func() {
-		_ = resp.Body.Close()
-	}()
 
 	if resp.StatusCode != http.StatusOK {
 		log.Fatalf("Failed to fetch CSV: HTTP %d", resp.StatusCode)
@@ -48,17 +54,20 @@ func main() {
 		log.Fatalf("Failed to read CSV header: %v", err)
 	}
 
-	if len(header) != 3 || header[0] != "asn" || header[1] != "handle" || header[2] != "description" {
+	if len(header) != 3 || header[0] != "asn" || header[1] != "handle" ||
+		header[2] != "description" {
 		log.Fatalf("Unexpected CSV header: %v", header)
 	}
 
 	// Read all records
 	var asInfos []ASInfo
+
 	for {
 		record, err := reader.Read()
-		if err == io.EOF {
+		if errors.Is(err, io.EOF) {
 			break
 		}
+
 		if err != nil {
 			log.Printf("Error reading CSV record: %v", err)
 
@@ -86,12 +95,18 @@ func main() {
 		})
 	}
 
+	// Closed here rather than deferred: log.Fatalf exits without running
+	// deferred calls.
+	_ = resp.Body.Close()
+
 	log.Printf("Parsed %d AS records", len(asInfos))
 
 	// Convert to JSON and output to stdout
 	encoder := json.NewEncoder(os.Stdout)
 	encoder.SetIndent("", "\t")
-	if err := encoder.Encode(asInfos); err != nil {
+
+	err = encoder.Encode(asInfos)
+	if err != nil {
 		log.Fatalf("Failed to encode JSON: %v", err)
 	}
 }