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_remote_pypi/main.tf

@@ -0,0 +1,23 @@
+terraform {
+  required_providers {
+    artifactapi = {
+      source  = "git.unkin.net/unkin/artifactapi"
+      version = "0.0.1"
+    }
+  }
+}
+
+provider "artifactapi" {
+  endpoint = "https://artifactapi.example.com"
+}
+
+# PyPI remote proxies a Python package index.
+# The provider knows /simple/ index pages are mutable; sdists and wheels are immutable.
+resource "artifactapi_remote_pypi" "pypi" {
+  name        = "pypi"
+  base_url    = "https://pypi.org"
+  description = "Python Package Index"
+
+  immutable_ttl = 0
+  mutable_ttl   = 900
+}