Fix Pairing Simulator: dog dropdowns were always empty

PairingSimulator read 'data.dogs' from GET /api/dogs, but that endpoint returns
a paginated { data, total, ... } object — the fallback silently produced an
empty list, so no sires or dams ever appeared. Same latent wrong-response-key
bug as the Start Heat Cycle female list fixed in 55d636b.

Switch to GET /api/dogs/all (unpaginated, kennel + external — no 50-dog page
cap) and surface load failures in the existing error card instead of
swallowing them.

Verified in-browser: dropdowns populate, parent-offspring pairing shows the
'Related' warning and computes COI 25.00% with common ancestor listed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/src/pages/PairingSimulator.jsx

@@ -15,14 +15,19 @@ export default function PairingSimulator() {
   const [geneticChecking, setGeneticChecking] = useState(false)
 
   useEffect(() => {
-    // include_external=1 ensures external sires/dams appear for pairing
+    // /all returns an unpaginated array of every active dog (kennel + external),
-    fetch('/api/dogs?include_external=1')
+    // so external sires/dams appear and nothing is cut off by pagination
-      .then(r => r.json())
+    fetch('/api/dogs/all')
+      .then(r => r.ok ? r.json() : Promise.reject(new Error(`HTTP ${r.status}`)))
       .then(data => {
-        setDogs(Array.isArray(data) ? data : (data.dogs || []))
+        setDogs(Array.isArray(data) ? data : (data.data || []))
+        setDogsLoading(false)
+      })
+      .catch((err) => {
+        console.error('Failed to load dogs for pairing:', err)
+        setError('Failed to load dogs — refresh to try again')
         setDogsLoading(false)
       })
-      .catch(() => setDogsLoading(false))
   }, [])
 
   // Check for direct relation whenever both sire and dam are selected