feat(client): add support for 8-bit hex color codes in CSS

This allows users to use #RRGGBBAA format in their style.css.
The client now detects 8-bit hex codes, transforms them into
GTK-compatible rgba() syntax, and loads the modified data
into the CSS provider.

- Added utility to detect 8-bit hex patterns.
- Added transformation logic to convert hex alpha to decimal.
- Intercepted CSS loading in Client::setupCss to handle the conversion.

src/util/has_8bit_hex.cpp

@@ -0,0 +1,15 @@
+#include <filesystem>
+#include <fstream>
+#include <regex>
+
+namespace fs = std::filesystem;
+
+bool has_8bit_hex(std::string file_path) {
+  std::ifstream f(file_path, std::ios::in | std::ios::binary);
+  const auto size = fs::file_size(file_path);
+  std::string result(size, '\0');
+  f.read(result.data(), size);
+  std::regex pattern(
+      R"((?:\#([a-fA-F0-9]{2})([a-fA-F0-9]{2})([a-fA-F0-9]{2})([a-fA-F0-9]{2})))");
+  return std::regex_search(result, pattern);
+}

src/util/transform_8bit_to_rgba.cpp

@@ -0,0 +1,41 @@
+#include <filesystem>
+#include <fstream>
+#include <iomanip>
+#include <regex>
+#include <sstream>
+namespace fs = std::filesystem;
+std::string transform_8bit_to_hex(std::string file_path) {
+  std::ifstream f(file_path, std::ios::in | std::ios::binary);
+  const auto size = fs::file_size(file_path);
+  std::string result(size, '\0');
+  f.read(result.data(), size);
+
+  std::regex pattern(
+      R"((?:\#([a-fA-F0-9]{2})([a-fA-F0-9]{2})([a-fA-F0-9]{2})([a-fA-F0-9]{2})))");
+  std::string final_output;
+
+  auto it = std::sregex_iterator(result.begin(), result.end(), pattern);
+  auto eof = std::sregex_iterator();
+  std::smatch match = *it;
+
+  while (it != eof) {
+
+    final_output += match.prefix().str();
+
+    int r = stoi(match[1].str(), nullptr, 16);
+    int g = stoi(match[2].str(), nullptr, 16);
+    int b = stoi(match[3].str(), nullptr, 16);
+    double a = (stoi(match[4].str(), nullptr, 16) / 255.0);
+
+    std::stringstream ss;
+    ss << "rgba(" << r << "," << g << "," << b << "," << std::fixed
+       << std::setprecision(2) << a << ")";
+    final_output += ss.str();
+
+    ++it;
+  }
+
+  final_output += match.suffix().str();
+
+  return final_output;
+}