appview: state: show most recent branch in pulls

Sorts branches by update time (and in same-repo comparisons we drop the
default branch) and preselects the most recent branch.

appview/pages/templates/repo/pulls/fragments/pullCompareBranches.html

···
                 class="p-1 border border-gray-200 bg-white dark:bg-gray-700 dark:text-white dark:border-gray-600"
             >
                 <option disabled selected>source branch</option>
+
+                {{ $recent := index .Branches 0 }}
                 {{ range .Branches }}
-                    <option value="{{ .Reference.Name }}" class="py-1">
+                    {{ $isRecent := eq .Reference.Name $recent.Reference.Name }}
+                    <option
+                        value="{{ .Reference.Name }}"
+                        {{ if $isRecent }}
+                            selected
+                        {{ end }}
+                        class="py-1"
+                    >
                         {{ .Reference.Name }}
+                        {{ if $isRecent }}(new){{ end }}
                     </option>
                 {{ end }}
             </select>

appview/pages/templates/repo/pulls/fragments/pullCompareForksBranches.html

···
             class="p-1 border border-gray-200 bg-white dark:bg-gray-700 dark:text-white dark:border-gray-600"
         >
             <option disabled selected>source branch</option>
+
+            {{ $recent := index .SourceBranches 0 }}
             {{ range .SourceBranches }}
-                <option value="{{ .Reference.Name }}" class="py-1">
+                {{ $isRecent := eq .Reference.Name $recent.Reference.Name }}
+                <option
+                    value="{{ .Reference.Name }}"
+                    {{ if $isRecent }}
+                        selected
+                    {{ end }}
+                    class="py-1"
+                >
                     {{ .Reference.Name }}
+                    {{ if $isRecent }}(new){{ end }}
                 </option>
             {{ end }}
         </select>

appview/state/pull.go

···
 	"io"
 	"log"
 	"net/http"
+	"sort"
 	"strconv"
 	"time"
 
···
 		return
 	}
 
+	branches := result.Branches
+	sort.Slice(branches, func(i int, j int) bool {
+		return branches[i].Commit.Committer.When.After(branches[j].Commit.Committer.When)
+	})
+
+	withoutDefault := []types.Branch{}
+	for _, b := range branches {
+		if b.IsDefault {
+			continue
+		}
+		withoutDefault = append(withoutDefault, b)
+	}
+
 	s.pages.PullCompareBranchesFragment(w, pages.PullCompareBranchesParams{
 		RepoInfo: f.RepoInfo(s, user),
-		Branches: result.Branches,
+		Branches: withoutDefault,
 	})
 }
 
···
 		log.Println("failed to parse target branches response:", err)
 		return
 	}
+
+	sourceBranches := sourceResult.Branches
+	sort.Slice(sourceBranches, func(i int, j int) bool {
+		return sourceBranches[i].Commit.Committer.When.After(sourceBranches[j].Commit.Committer.When)
+	})
 
 	s.pages.PullCompareForkBranchesFragment(w, pages.PullCompareForkBranchesParams{
 		RepoInfo:       f.RepoInfo(s, user),