feat: add label multi-select to Create Issue form

Add dynamic label selection when creating a new issue:
- New GET /issues/new/labels endpoint returns label checkboxes for a repo
- When a repo is selected, labels are fetched via HTMX and displayed as
  checkboxes with colored label badges
- CreateIssue handler now parses label_ids from form and passes them to
  the Gitea API
- Shows "No labels available" message when repo has no labels

Closes leeworks-agents/gitea-mobile#67

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

internal/handlers/handlers.go

@@ -39,6 +39,7 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	// Issues.
 	mux.HandleFunc("GET /issues", h.ListIssues)
 	mux.HandleFunc("GET /issues/new", h.NewIssue)
+	mux.HandleFunc("GET /issues/new/labels", h.NewIssueLabels)
 	mux.HandleFunc("POST /issues", h.CreateIssue)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/labels", h.ApplyLabels)
 	mux.HandleFunc("POST /issues/{owner}/{repo}/{index}/close", h.CloseIssue)
@@ -567,6 +568,38 @@ func (h *Handler) NewIssue(w http.ResponseWriter, r *http.Request) {
 	renderPage(w, r, "New Issue", "issues", buf.String())
 }
 
+// NewIssueLabels handles GET /issues/new/labels — returns label checkboxes for a repo.
+func (h *Handler) NewIssueLabels(w http.ResponseWriter, r *http.Request) {
+	token := getToken(r)
+	owner := r.URL.Query().Get("owner")
+	repo := r.URL.Query().Get("repo")
+
+	if owner == "" || repo == "" {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		fmt.Fprint(w, `<span class="empty">Select a repository first.</span>`)
+		return
+	}
+
+	labels, err := h.Client.GetRepoLabels(r.Context(), token, owner, repo)
+	if err != nil {
+		slog.Error("failed to fetch labels", "error", err, "owner", owner, "repo", repo)
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		fmt.Fprint(w, `<span class="empty">Error loading labels.</span>`)
+		return
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	if len(labels) == 0 {
+		fmt.Fprint(w, `<span class="empty">No labels available for this repository.</span>`)
+		return
+	}
+
+	for _, l := range labels {
+		fmt.Fprintf(w, `<label style="display:inline-block;margin:0.25rem 0.5rem 0.25rem 0;cursor:pointer;"><input type="checkbox" name="label_ids" value="%d" style="margin-right:0.25rem;"> <span class="label" style="color:#%s;border:1px solid #%s">%s</span></label>`,
+			l.ID, template.HTMLEscapeString(l.Color), template.HTMLEscapeString(l.Color), template.HTMLEscapeString(l.Name))
+	}
+}
+
 // CreateIssue handles POST /issues.
 func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 	token := getToken(r)
@@ -580,6 +613,15 @@ func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 	title := r.FormValue("title")
 	body := r.FormValue("body")
 
+	// Parse label IDs from form checkboxes.
+	var labelIDs []int64
+	for _, idStr := range r.Form["label_ids"] {
+		id, err := strconv.ParseInt(idStr, 10, 64)
+		if err == nil {
+			labelIDs = append(labelIDs, id)
+		}
+	}
+
 	if owner == "" || repo == "" || title == "" {
 		if isHTMX(r) {
 			w.Header().Set("Content-Type", "text/html; charset=utf-8")
@@ -591,7 +633,7 @@ func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	issue, err := h.Client.CreateIssue(r.Context(), token, owner, repo, title, body, nil)
+	issue, err := h.Client.CreateIssue(r.Context(), token, owner, repo, title, body, labelIDs)
 	if err != nil {
 		slog.Error("failed to create issue", "error", err)
 		if isHTMX(r) {