refactor: make crawler importable and add export pipeline

Move monkeyd and pdfout out of internal/ so other modules can import them,
and add export.Export, which holds the crawl-to-PDF sequence the CLI used to
inline. The CLI now parses flags and delegates, so an embedding program gets
the same defaults and validation.

monkeyd-crawler/monkeyd/html_nodes.go

@@ -0,0 +1,95 @@
+package monkeyd
+
+import (
+	"strings"
+
+	"golang.org/x/net/html"
+)
+
+// attr returns the value of the named attribute, or "" when absent.
+func attr(n *html.Node, name string) string {
+	for _, a := range n.Attr {
+		if a.Key == name {
+			return a.Val
+		}
+	}
+	return ""
+}
+
+// hasClass reports whether the node carries the given class token.
+func hasClass(n *html.Node, class string) bool {
+	for _, tok := range strings.Fields(attr(n, "class")) {
+		if tok == class {
+			return true
+		}
+	}
+	return false
+}
+
+// findNode returns the first node in document order satisfying match.
+func findNode(root *html.Node, match func(*html.Node) bool) *html.Node {
+	if match(root) {
+		return root
+	}
+	for c := root.FirstChild; c != nil; c = c.NextSibling {
+		if found := findNode(c, match); found != nil {
+			return found
+		}
+	}
+	return nil
+}
+
+// findAllNodes returns every node satisfying match, in document order.
+func findAllNodes(root *html.Node, match func(*html.Node) bool) []*html.Node {
+	var out []*html.Node
+	var walk func(*html.Node)
+	walk = func(n *html.Node) {
+		if match(n) {
+			out = append(out, n)
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			walk(c)
+		}
+	}
+	walk(root)
+	return out
+}
+
+// elementByID finds an element by its id attribute.
+func elementByID(root *html.Node, id string) *html.Node {
+	return findNode(root, func(n *html.Node) bool {
+		return n.Type == html.ElementNode && attr(n, "id") == id
+	})
+}
+
+// elementByTag finds the first element with the given tag name.
+func elementByTag(root *html.Node, tag string) *html.Node {
+	return findNode(root, func(n *html.Node) bool {
+		return n.Type == html.ElementNode && n.Data == tag
+	})
+}
+
+// nodeText collects the descendant text of a node with whitespace collapsed.
+func nodeText(n *html.Node) string {
+	if n == nil {
+		return ""
+	}
+	var b strings.Builder
+	var walk func(*html.Node)
+	walk = func(n *html.Node) {
+		if n.Type == html.TextNode {
+			b.WriteString(n.Data)
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			walk(c)
+		}
+	}
+	walk(n)
+	return collapseSpaces(b.String())
+}
+
+// collapseSpaces trims the string and reduces every whitespace run, including
+// the non-breaking spaces the site emits as  , to a single space.
+func collapseSpaces(s string) string {
+	return strings.Join(strings.Fields(s), " ")
+}