docs: add README, per-resource examples, unit tests, CI, and pre-commit

- Add README.md with provider docs, resource/data-source reference, and
  development instructions
- Reorganize examples into per-resource-type subdirectories following
  Terraform provider conventions, add missing pypi/npm/puppet examples
- Add unit tests for helpers, HTTP client, model conversions, and
  provider registration
- Add Woodpecker CI pipelines for lint, test, and build
- Add pre-commit config with standard and Go-specific hooks

examples/resources/artifactapi_virtual/main.tf

@@ -0,0 +1,45 @@
+terraform {
+  required_providers {
+    artifactapi = {
+      source  = "git.unkin.net/unkin/artifactapi"
+      version = "0.0.1"
+    }
+  }
+}
+
+provider "artifactapi" {
+  endpoint = "https://artifactapi.example.com"
+}
+
+# Helm remotes to be merged into a virtual repository
+resource "artifactapi_remote_helm" "jetstack" {
+  name        = "jetstack"
+  base_url    = "https://charts.jetstack.io"
+  description = "Jetstack Helm charts (cert-manager)"
+
+  immutable_ttl = 0
+  mutable_ttl   = 3600
+}
+
+resource "artifactapi_remote_helm" "hashicorp_helm" {
+  name        = "hashicorp-helm"
+  base_url    = "https://helm.releases.hashicorp.com"
+  description = "HashiCorp Helm charts"
+
+  immutable_ttl = 0
+  mutable_ttl   = 3600
+}
+
+# Virtual repository merges multiple remotes of the same package type
+# into a single endpoint. Earlier members have higher priority for
+# duplicate entries.
+resource "artifactapi_virtual" "helm" {
+  name         = "helm"
+  package_type = "helm"
+  description  = "All Helm repos merged"
+
+  members = [
+    artifactapi_remote_helm.jetstack.name,
+    artifactapi_remote_helm.hashicorp_helm.name,
+  ]
+}