Add notebook delete, fix button styling, rename Share button

- Add delete notebook handler with ownership check and CASCADE delete
- Rename "Create Share Link" to "Share"
- Fix action button heights: use inline-flex + align-items for
  consistent sizing across <a> and <button> elements

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

internal/webserver/handlers.go

@@ -248,6 +248,23 @@ func (ws *WebServer) handleCreateShare(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, fmt.Sprintf("/notebooks/%d", id), http.StatusFound)
 }
 
+func (ws *WebServer) handleDeleteNotebook(w http.ResponseWriter, r *http.Request) {
+	userID := r.Context().Value(userIDKey).(int64)
+	id, _ := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
+
+	// Verify ownership before deleting.
+	var ownerID int64
+	err := ws.db.QueryRow("SELECT user_id FROM notebooks WHERE id = ?", id).Scan(&ownerID)
+	if err != nil || ownerID != userID {
+		http.Error(w, "Not found", http.StatusNotFound)
+		return
+	}
+
+	// CASCADE deletes pages, strokes, and share_links.
+	_, _ = ws.db.Exec("DELETE FROM notebooks WHERE id = ?", id)
+	http.Redirect(w, r, "/notebooks", http.StatusFound)
+}
+
 func (ws *WebServer) handleRevokeShare(w http.ResponseWriter, r *http.Request) {
 	id, _ := strconv.ParseInt(chi.URLParam(r, "id"), 10, 64)
 	token := r.FormValue("token")

internal/webserver/server.go

@@ -112,6 +112,7 @@ func Start(cfg Config) (*http.Server, error) {
 		r.Get("/notebooks/{id}/pages/{num}/svg", ws.handlePageSVG)
 		r.Get("/notebooks/{id}/pages/{num}/jpg", ws.handlePageJPG)
 		r.Get("/notebooks/{id}/pdf", ws.handleNotebookPDF)
+		r.Post("/notebooks/{id}/delete", ws.handleDeleteNotebook)
 		r.Post("/notebooks/{id}/share", ws.handleCreateShare)
 		r.Post("/notebooks/{id}/share/revoke", ws.handleRevokeShare)
 		r.Get("/logout", ws.handleLogout)