refactor(cava): fix thread-safety, resource leaks, and style violations

Comprehensive refactor of the cava module backend and frontends.

Style & naming
- Rename Cava -> CavaRaw; snake_case methods -> lowerCamelCase
- Replace NULL with nullptr; replace C-style casts with static_cast
- Add explicit standard-library includes (<memory>, <string>, <chrono>)
- Fix missing trailing underscores on member variables

Architecture
- Remove Gtk::GLArea multiple inheritance in CavaGLSL (composition)
- Return std::unique_ptr from factory; add doAction() to GLSL variant
- Encapsulate thread timing arithmetic in AdaptiveDelay struct

Thread safety & correctness
- Replace raw sigc::signal with SafeSignal for cross-thread marshalling
- Fix data race between loadConfig() and out_thread_ (recursive_mutex)
- Fix audio_raw shallow-copy use-after-free via deep-copy AudioRaw payload
- Make loadConfig() exception-safe with CavaConfigGuard RAII
- Fix blocking read_thread_ race on shutdown (condition_variable + timeout join)
- Fix isSilent() data race (acquire pthread mutex)
- Eliminate doUpdate() recursion (iteration instead)
- Guard audio_raw_clean() against uninitialized state
- Fix format-icons underflow and cava_config buffer overflow
- Store config by value to prevent dangling references on reload
- Cache frontend config and refresh on runtime changes
- Fix signed-char icon lookup bug on x86
- Prevent Json::Value mutation bloat via const-ref lookups
- Broaden exception catches in worker threads (std::exception)

Resource management & GL robustness
- Fix OpenGL resource leaks (persist VBO/IBO/VAO; explicit destructor cleanup)
- Fix shader error handling crashes (valid infoLog allocation)
- Cache uniform locations instead of querying per frame
- Fix gradient color uninitialized stack memory (zero-init + clamped count)
- Fix shader time uniform integer division bug (float arithmetic)
- Add explicit VAO bind in onRender()
- Handle runtime surface config changes independently of shader changes
- Clamp negative gradient_count before GL upload

Follow-up
- Singleton API split (inst() + configure()) intentionally deferred to a
  dedicated PR because it changes the public constructor contract.

include/modules/cava/cava_frontend.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <memory>
+
 #ifdef HAVE_LIBCAVA
 #include "cavaRaw.hpp"
 #include "cava_backend.hpp"
@@ -9,16 +11,16 @@
 #endif
 
 namespace waybar::modules::cava {
-AModule* getModule(const std::string& id, const Json::Value& config) {
+inline std::unique_ptr<AModule> getModule(const std::string& id, const Json::Value& config) {
 #ifdef HAVE_LIBCAVA
   const std::shared_ptr<CavaBackend> backend_{waybar::modules::cava::CavaBackend::inst(config)};
-  switch (backend_->getPrm()->output) {
+  switch (backend_->getPrm().output) {
 #ifdef HAVE_LIBCAVAGLSL
     case ::cava::output_method::OUTPUT_SDL_GLSL:
-      return new waybar::modules::cava::CavaGLSL(id, config);
+      return std::make_unique<waybar::modules::cava::CavaGLSL>(id, config);
 #endif
     default:
-      return new waybar::modules::cava::Cava(id, config);
+      return std::make_unique<waybar::modules::cava::CavaRaw>(id, config);
   }
 #else
   throw std::runtime_error("Unknown module");