feat: add GET /issues/new handler to serve create-issue form

Register GET /issues/new route and implement NewIssue handler that
fetches orgs/repos via ListOrgsAndRepos and renders the existing
create_issue.html template. Supports HTMX partial responses.

Closes leeworks-agents/gitea-mobile#28

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

internal/handlers/handlers.go

@@ -38,6 +38,7 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 
 	// Issues.
 	mux.HandleFunc("GET /issues", h.ListIssues)
+	mux.HandleFunc("GET /issues/new", h.NewIssue)
 	mux.HandleFunc("POST /issues", h.CreateIssue)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/labels", h.ApplyLabels)
 
@@ -444,6 +445,41 @@ func (h *Handler) PullDetail(w http.ResponseWriter, r *http.Request) {
 	renderPage(w, r, fmt.Sprintf("PR #%d", index), "pulls", buf.String())
 }
 
+// NewIssue handles GET /issues/new — renders the create-issue form.
+func (h *Handler) NewIssue(w http.ResponseWriter, r *http.Request) {
+	token := getToken(r)
+
+	repos, err := h.Client.ListOrgsAndRepos(r.Context(), token)
+	if err != nil {
+		slog.Error("failed to list repos for new issue form", "error", err)
+		renderPage(w, r, "New Issue", "issues",
+			`<h1>New Issue</h1><p class="empty">Error loading repositories.</p>`)
+		return
+	}
+
+	tmpl, err := template.ParseFiles("internal/templates/create_issue.html")
+	if err != nil {
+		slog.Error("failed to parse create_issue template", "error", err)
+		http.Error(w, "template error", http.StatusInternalServerError)
+		return
+	}
+
+	type templateData struct {
+		Repos map[string][]giteaclient.Repo
+	}
+
+	data := templateData{Repos: repos}
+
+	var buf strings.Builder
+	if err := tmpl.ExecuteTemplate(&buf, "content", data); err != nil {
+		slog.Error("failed to execute create_issue template", "error", err)
+		http.Error(w, "template error", http.StatusInternalServerError)
+		return
+	}
+
+	renderPage(w, r, "New Issue", "issues", buf.String())
+}
+
 // CreateIssue handles POST /issues.
 func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 	token := getToken(r)