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).

flake.nix

@@ -26,7 +26,7 @@
           pname = "puppy-tracker-server";
           version = "0.2.0";
           src = ./server;
-          vendorHash = "sha256-z9Kf7i4WfLAHmceRi8T42+uMitjxEzr0pmOn+STpsAU=";
+          vendorHash = "sha256-J1lYhwbaRh2PeAh3SzyB9WgUZa1gCNXBWdaJ5isUedA=";
           # Pure-Go build for a tiny static binary.
           env.CGO_ENABLED = "0";
           ldflags = [ "-s" "-w" ];