feat: add close/reopen and comment actions to issue detail view

Add SetIssueState client method and handler for toggling issue state
between open and closed via PATCH API. Add AddComment client method
wrapping PostComment. Register new routes POST /issues/{owner}/{repo}/{index}/state
and POST /issues/{owner}/{repo}/{index}/comments. Update issue_detail.html
template with comment form (HTMX inline append) and close/reopen button
(HTMX inline swap of state badge).

Closes leeworks-agents/gitea-mobile#29

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

internal/templates/issue_detail.html

@@ -3,7 +3,15 @@
 
 <div class="card">
   <div class="card-meta">
-    <span class="state-open">{{.Issue.State}}</span>
+    <span id="state-section">
+      {{if eq .Issue.State "closed"}}
+      <span class="state-closed" id="issue-state">{{.Issue.State}}</span>
+      <button class="btn btn-secondary" hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/state" hx-vals='{"state":"open"}' hx-target="#state-section" hx-swap="innerHTML">Reopen Issue</button>
+      {{else}}
+      <span class="state-open" id="issue-state">{{.Issue.State}}</span>
+      <button class="btn btn-danger" hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/state" hx-vals='{"state":"closed"}' hx-target="#state-section" hx-swap="innerHTML">Close Issue</button>
+      {{end}}
+    </span>
     <span>{{.Issue.RepoOwner}}/{{.Issue.RepoName}} #{{.Issue.Number}}</span>
     {{range .Issue.Labels}}
     <span class="label" style="color:#{{.Color}};border:1px solid #{{.Color}}">{{.Name}}</span>
@@ -18,6 +26,7 @@
 
 {{if .Comments}}
 <h2>Comments</h2>
+<div id="comments-list">
 {{range .Comments}}
 <div class="comment">
   <div class="comment-header">
@@ -27,8 +36,19 @@
   <div class="comment-body">{{.Body}}</div>
 </div>
 {{end}}
+</div>
+{{else}}
+<div id="comments-list"></div>
 {{end}}
 
+<div class="card" style="margin-top:1rem;">
+  <h2>Add Comment</h2>
+  <form hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/comments" hx-target="#comments-list" hx-swap="beforeend" hx-on::after-request="if(event.detail.successful) this.reset()">
+    <textarea name="body" rows="4" placeholder="Write a comment..." required style="width:100%;margin-bottom:0.5rem;"></textarea>
+    <button type="submit" class="btn btn-primary" style="width:auto;padding:0.5rem 1rem;">Comment</button>
+  </form>
+</div>
+
 <div class="card" style="margin-top:1rem;">
   <h2>Actions</h2>
   <form hx-post="/issues/{{.Issue.RepoOwner}}/{{.Issue.RepoName}}/{{.Issue.Number}}/labels" hx-swap="outerHTML" style="margin-bottom:0.5rem;">