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).

README.md

@@ -94,6 +94,22 @@ events, profile and photos.
   when you pass `-secure-cookies` (enable it behind a TLS proxy), so passwords
   aren't sent in the clear.
 
+## Pedigree lookup
+
+The 🌳 page looks up a dog in **SKK Hunddata** by ISO chip number or
+registration number and renders its ancestry as a tree.
+
+- SKK has no public API, so the server drives the interactive site the way a
+  browser would: it resolves the input to SKK's internal dog id, fetches the
+  pedigree page (7 generations per request), and follows each generation's leaves
+  deeper. A lookup returns the first generations immediately and keeps crawling in
+  the background; the client polls and fills the tree in as ancestors arrive.
+- Because a deep crawl is dozens of sequential upstream requests, finished trees
+  are cached per dog in the `pedigree_cache` table (pedigrees don't change), so a
+  dog is only ever crawled once and repeat lookups are instant.
+- The lookup is behind auth like the rest of `/api/*`, and is **online-only** —
+  it needs to reach SKK.
+
 ## Use it on NixOS
 
 In your system flake: