fix: add pagination to unbounded GET endpoints

All list endpoints now accept ?page and ?limit (default 50, max 200) and
return { data, total, page, limit } instead of a bare array, preventing
memory and performance failures at scale.

- GET /api/dogs: adds pagination, server-side search (?search) and sex
  filter (?sex), and a stats aggregate (total/males/females) for the
  Dashboard to avoid counting from the array
- GET /api/litters: adds pagination; also fixes N+1 query by fetching
  all puppies for the current page in a single query instead of one per
  litter
- DogList: moves search/sex filtering server-side with 300ms debounce;
  adds Prev/Next pagination controls
- LitterList: uses paginated response; adds Prev/Next pagination controls
- Dashboard: reads counts from stats/total fields instead of array length
- LitterDetail, LitterForm: switch dogs fetch to /api/dogs/all (complete
  list, no pagination, for sire/dam dropdowns)
- DogForm: updates litters fetch to use paginated response shape

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/src/pages/DogList.jsx

@@ -1,57 +1,69 @@
-import { useEffect, useState } from 'react'
+import { useEffect, useState, useRef } from 'react'
 import { Link, useNavigate } from 'react-router-dom'
 import { Dog, Plus, Search, Calendar, Hash, ArrowRight, Trash2 } from 'lucide-react'
 import axios from 'axios'
 import DogForm from '../components/DogForm'
 import { ChampionBadge, ChampionBloodlineBadge } from '../components/ChampionBadge'
 
+const LIMIT = 50
+
 function DogList() {
   const [dogs, setDogs] = useState([])
-  const [filteredDogs, setFilteredDogs] = useState([])
+  const [total, setTotal] = useState(0)
+  const [page, setPage] = useState(1)
   const [search, setSearch] = useState('')
   const [sexFilter, setSexFilter] = useState('all')
   const [loading, setLoading] = useState(true)
   const [showAddModal, setShowAddModal] = useState(false)
   const [deleteTarget, setDeleteTarget] = useState(null)  // { id, name }
   const [deleting, setDeleting] = useState(false)
+  const searchTimerRef = useRef(null)
 
-  useEffect(() => { fetchDogs() }, [])
-  useEffect(() => { filterDogs() }, [dogs, search, sexFilter])
+  useEffect(() => { fetchDogs(1, '', 'all') }, [])  // eslint-disable-line
 
-  const fetchDogs = async () => {
+  const fetchDogs = async (p, q, s) => {
+    setLoading(true)
     try {
-      const res = await axios.get('/api/dogs')
-      setDogs(res.data)
-      setLoading(false)
+      const params = { page: p, limit: LIMIT }
+      if (q) params.search = q
+      if (s !== 'all') params.sex = s
+      const res = await axios.get('/api/dogs', { params })
+      setDogs(res.data.data)
+      setTotal(res.data.total)
+      setPage(p)
     } catch (error) {
       console.error('Error fetching dogs:', error)
+    } finally {
       setLoading(false)
     }
   }
 
-  const filterDogs = () => {
-    let filtered = dogs
-    if (search) {
-      filtered = filtered.filter(dog =>
-        dog.name.toLowerCase().includes(search.toLowerCase()) ||
-        (dog.registration_number && dog.registration_number.toLowerCase().includes(search.toLowerCase()))
-      )
-    }
-    if (sexFilter !== 'all') {
-      filtered = filtered.filter(dog => dog.sex === sexFilter)
-    }
-    setFilteredDogs(filtered)
+  const handleSearchChange = (value) => {
+    setSearch(value)
+    if (searchTimerRef.current) clearTimeout(searchTimerRef.current)
+    searchTimerRef.current = setTimeout(() => fetchDogs(1, value, sexFilter), 300)
   }
 
-  const handleSave = () => { fetchDogs() }
+  const handleSexChange = (value) => {
+    setSexFilter(value)
+    fetchDogs(1, search, value)
+  }
+
+  const handleClearFilters = () => {
+    setSearch('')
+    setSexFilter('all')
+    fetchDogs(1, '', 'all')
+  }
+
+  const handleSave = () => { fetchDogs(page, search, sexFilter) }
 
   const handleDelete = async () => {
     if (!deleteTarget) return
     setDeleting(true)
     try {
       await axios.delete(`/api/dogs/${deleteTarget.id}`)
-      setDogs(prev => prev.filter(d => d.id !== deleteTarget.id))
       setDeleteTarget(null)
+      fetchDogs(page, search, sexFilter)
     } catch (err) {
       console.error('Delete failed:', err)
       alert('Failed to delete dog. Please try again.')
@@ -60,6 +72,8 @@ function DogList() {
     }
   }
 
+  const totalPages = Math.ceil(total / LIMIT)
+
   const calculateAge = (birthDate) => {
     if (!birthDate) return null
     const today = new Date()
@@ -85,7 +99,7 @@ function DogList() {
         <div>
           <h1 style={{ marginBottom: '0.25rem' }}>Dogs</h1>
           <p style={{ color: 'var(--text-secondary)', fontSize: '0.875rem' }}>
-            {filteredDogs.length} {filteredDogs.length === 1 ? 'dog' : 'dogs'}
+            {total} {total === 1 ? 'dog' : 'dogs'}
             {search || sexFilter !== 'all' ? ' matching filters' : ' total'}
           </p>
         </div>
@@ -105,11 +119,11 @@ function DogList() {
               className="input"
               placeholder="Search by name or registration..."
               value={search}
-              onChange={(e) => setSearch(e.target.value)}
+              onChange={(e) => handleSearchChange(e.target.value)}
               style={{ paddingLeft: '2.75rem' }}
             />
           </div>
-          <select className="input" value={sexFilter} onChange={(e) => setSexFilter(e.target.value)} style={{ width: '140px' }}>
+          <select className="input" value={sexFilter} onChange={(e) => handleSexChange(e.target.value)} style={{ width: '140px' }}>
             <option value="all">All Dogs</option>
             <option value="male">Males ♂</option>
             <option value="female">Females ♀</option>
@@ -117,7 +131,7 @@ function DogList() {
           {(search || sexFilter !== 'all') && (
             <button
               className="btn btn-ghost"
-              onClick={() => { setSearch(''); setSexFilter('all') }}
+              onClick={handleClearFilters}
               style={{ padding: '0.625rem 1rem', fontSize: '0.875rem' }}
             >
               Clear
@@ -127,7 +141,7 @@ function DogList() {
       </div>
 
       {/* Dogs List */}
-      {filteredDogs.length === 0 ? (
+      {dogs.length === 0 ? (
         <div className="card" style={{ textAlign: 'center', padding: '4rem 2rem' }}>
           <Dog size={64} style={{ color: 'var(--text-muted)', margin: '0 auto 1rem', opacity: 0.5 }} />
           <h3 style={{ marginBottom: '0.5rem' }}>
@@ -147,7 +161,7 @@ function DogList() {
         </div>
       ) : (
         <div style={{ display: 'grid', gap: '1rem' }}>
-          {filteredDogs.map(dog => (
+          {dogs.map(dog => (
             <div
               key={dog.id}
               className="card"
@@ -313,6 +327,31 @@ function DogList() {
         </div>
       )}
 
+      {/* Pagination */}
+      {totalPages > 1 && (
+        <div style={{ display: 'flex', justifyContent: 'center', alignItems: 'center', gap: '1rem', marginTop: '1.5rem' }}>
+          <button
+            className="btn btn-ghost"
+            onClick={() => fetchDogs(page - 1, search, sexFilter)}
+            disabled={page <= 1 || loading}
+            style={{ padding: '0.5rem 1rem' }}
+          >
+            Previous
+          </button>
+          <span style={{ color: 'var(--text-secondary)', fontSize: '0.875rem' }}>
+            Page {page} of {totalPages}
+          </span>
+          <button
+            className="btn btn-ghost"
+            onClick={() => fetchDogs(page + 1, search, sexFilter)}
+            disabled={page >= totalPages || loading}
+            style={{ padding: '0.5rem 1rem' }}
+          >
+            Next
+          </button>
+        </div>
+      )}
+
       {/* Add Dog Modal */}
       {showAddModal && (
         <DogForm