feat: add open/closed state filter to PR list view

Mirror the existing issues state filter pattern: read state query param
(default "open"), pass it to ListAllPullRequests instead of hardcoded
"open", and add a state select widget to the pulls filter bar with
proper hx-include for HTMX partial reloads and infinite scroll.

Closes leeworks-agents/gitea-mobile#72

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/templates/pulls.html

@@ -17,7 +17,7 @@
   </div>
   {{end}}
   {{if .HasMore}}
-  <div class="scroll-sentinel" hx-get="/pulls?page={{.NextPage}}&org={{.SelectedOrg}}" hx-trigger="revealed" hx-swap="outerHTML" hx-target="this">
+  <div class="scroll-sentinel" hx-get="/pulls?page={{.NextPage}}&org={{.SelectedOrg}}&state={{.SelectedState}}" hx-trigger="revealed" hx-swap="outerHTML" hx-target="this">
     <div class="spinner htmx-indicator"></div>
   </div>
   {{end}}
@@ -27,18 +27,22 @@
 <h1>Pull Requests</h1>
 
 <div class="filter-bar">
-  <select name="org" hx-get="/pulls" hx-trigger="change" hx-target="#main-content" hx-swap="innerHTML" hx-push-url="true">
+  <select name="org" hx-get="/pulls" hx-trigger="change" hx-target="#main-content" hx-swap="innerHTML" hx-push-url="true" hx-include="[name='state']">
     <option value="">All orgs</option>
     {{range .Orgs}}
     <option value="{{.}}" {{if eq . $.SelectedOrg}}selected{{end}}>{{.}}</option>
     {{end}}
   </select>
+  <select name="state" hx-get="/pulls" hx-trigger="change" hx-target="#main-content" hx-swap="innerHTML" hx-push-url="true" hx-include="[name='org']">
+    <option value="open" {{if eq .SelectedState "open"}}selected{{end}}>Open</option>
+    <option value="closed" {{if eq .SelectedState "closed"}}selected{{end}}>Closed</option>
+  </select>
 </div>
 
 {{if .Error}}
 <p class="empty">{{.Error}}</p>
 {{else if not .Pulls}}
-<p class="empty">No open pull requests found.</p>
+<p class="empty">No {{.SelectedState}} pull requests found.</p>
 {{else}}
 <div id="pull-list">
   {{template "cards" .}}