Add pedigree lookup and ancestry tree page

New 🌳 Pedigree view: enter a dog's ISO chip or SKK registration number
and see its ancestry rendered as a tree. SKK has no public API, so the
server drives SKK Hunddata like a browser: it resolves the input to an
internal hundid via the Hund_sok.aspx/HundData page-method, renders 7
generations per pedigree page, parses the rowspan grid into ahnentafel
positions, and follows each generation's leaves deeper by reading their
hundid out of the __doPostBack response viewstate.

A lookup returns the first 7 generations immediately and crawls deeper in
the background; the client polls and fills the tree in as ancestors
arrive. Finished trees are cached per dog in a new pedigree_cache table
(pedigrees don't change), so a dog is crawled once and repeats are instant.
The endpoints sit behind auth like the rest of /api/*, and the crawl is
kept polite (warmed session, delay between requests, one coalesced job per
dog, hard caps).

server/htmlutil.go

@@ -0,0 +1,102 @@
+package main
+
+// Small helpers over golang.org/x/net/html for walking the SKK pedigree markup.
+
+import (
+	"strings"
+
+	"golang.org/x/net/html"
+)
+
+func attr(n *html.Node, key string) string {
+	for _, a := range n.Attr {
+		if a.Key == key {
+			return a.Val
+		}
+	}
+	return ""
+}
+
+// findByID returns the first element in the tree with the given id attribute.
+func findByID(n *html.Node, id string) *html.Node {
+	if n.Type == html.ElementNode && attr(n, "id") == id {
+		return n
+	}
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if got := findByID(c, id); got != nil {
+			return got
+		}
+	}
+	return nil
+}
+
+// descendants returns every element with the given tag anywhere under n, in
+// document order.
+func descendants(n *html.Node, tag string) []*html.Node {
+	var out []*html.Node
+	var walk func(*html.Node)
+	walk = func(x *html.Node) {
+		for c := x.FirstChild; c != nil; c = c.NextSibling {
+			if c.Type == html.ElementNode && c.Data == tag {
+				out = append(out, c)
+			}
+			walk(c)
+		}
+	}
+	walk(n)
+	return out
+}
+
+// directChildElements returns the immediate element children of n with the tag.
+func directChildElements(n *html.Node, tag string) []*html.Node {
+	var out []*html.Node
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if c.Type == html.ElementNode && c.Data == tag {
+			out = append(out, c)
+		}
+	}
+	return out
+}
+
+// findElement returns the first descendant element with the given tag.
+func findElement(n *html.Node, tag string) *html.Node {
+	els := descendants(n, tag)
+	if len(els) == 0 {
+		return nil
+	}
+	return els[0]
+}
+
+// text concatenates all text under n.
+func text(n *html.Node) string {
+	var sb strings.Builder
+	var walk func(*html.Node)
+	walk = func(x *html.Node) {
+		if x.Type == html.TextNode {
+			sb.WriteString(x.Data)
+		}
+		for c := x.FirstChild; c != nil; c = c.NextSibling {
+			walk(c)
+		}
+	}
+	walk(n)
+	return sb.String()
+}
+
+// normalizeText trims and collapses internal whitespace.
+func normalizeText(s string) string {
+	return strings.TrimSpace(wsRE.ReplaceAllString(s, " "))
+}
+
+// findBoldSpan returns the normalized text of the first bold <span> (how subject
+// cells carry the registration number), or "".
+func findBoldSpan(n *html.Node) string {
+	for _, sp := range descendants(n, "span") {
+		if strings.Contains(strings.ReplaceAll(attr(sp, "style"), " ", ""), "font-weight:bold") {
+			if t := normalizeText(text(sp)); t != "" {
+				return t
+			}
+		}
+	}
+	return ""
+}