Fix duplicate explorer buttons + populate share explorer data

1. Remove server-side explorer nav link injection that duplicated
   the client-side JS injection on dashboard and share pages.

2. Add heads/verified_heads/tails/verified_tails/my_share_hashes
   to sharechain_stats_fn so the classic page's share explorer
   section shows actual data instead of empty fields.

Author: frstrtr

src/c2pool/c2pool_refactored.cpp

@@ -2951,6 +2951,35 @@ int main(int argc, char* argv[]) {
                     });
                 }
                 result["timeline"] = tl;
+
+                // Share explorer fields for classic page (/web/heads etc.)
+                {
+                    auto& verified = p2p_node->tracker().verified;
+
+                    nlohmann::json heads_arr = nlohmann::json::array();
+                    for (auto& [h, t] : chain.get_heads())
+                        heads_arr.push_back(h.GetHex());
+                    result["heads"] = std::move(heads_arr);
+
+                    nlohmann::json vheads_arr = nlohmann::json::array();
+                    for (auto& [h, t] : verified.get_heads())
+                        vheads_arr.push_back(h.GetHex());
+                    result["verified_heads"] = std::move(vheads_arr);
+
+                    nlohmann::json tails_arr = nlohmann::json::array();
+                    for (auto& [t, hs] : chain.get_tails())
+                        tails_arr.push_back(t.GetHex());
+                    result["tails"] = std::move(tails_arr);
+
+                    nlohmann::json vtails_arr = nlohmann::json::array();
+                    for (auto& [t, hs] : verified.get_tails())
+                        vtails_arr.push_back(t.GetHex());
+                    result["verified_tails"] = std::move(vtails_arr);
+
+                    // my_share_hashes: empty for now (no local share tracking yet)
+                    result["my_share_hashes"] = nlohmann::json::array();
+                }
+
                 return result;
             });
 

src/core/web_server.cpp

@@ -620,19 +620,11 @@ void HttpSession::process_request()
                             }
                         }
 
-                        // Inject explorer nav link if configured
-                        const auto& explorer_url = mining_interface_->get_explorer_url();
-                        if (!explorer_url.empty() && mining_interface_->is_explorer_enabled()
-                            && (ext == ".html" || ext == ".htm"))
-                        {
-                            // Find "Classic" nav link and insert Explorer after it
-                            auto pos = contents.find(R"(>Classic</a>)");
-                            if (pos != std::string::npos) {
-                                pos += 12;  // skip ">Classic</a>"
-                                std::string link = "\n        <a href=\"" + explorer_url + "\" target=\"_blank\">Explorer</a>";
-                                contents.insert(pos, link);
-                            }
-                        }
+                        // Explorer nav link injection removed — each HTML page has
+                        // client-side JS that checks currency_info.explorer_enabled
+                        // and injects the link dynamically. Server-side injection was
+                        // fragile (depended on exact ">Classic</a>" text) and caused
+                        // duplicate buttons on pages that had both mechanisms.
 
                         response.set(http::field::content_type, mime);
                         response.set(http::field::cache_control, "public, max-age=3600");