feat: audio mixer, Audio app, fix Installer crash

kernel/src/Drivers/Audio/IntelHda.cpp

@@ -5,6 +5,7 @@
 */
 
 #include "IntelHda.hpp"
+#include "Mixer.hpp"
 #include <Memory/PageFrameAllocator.hpp>
 #include <Memory/HHDM.hpp>
 #include <Memory/Paging.hpp>
@@ -840,12 +841,14 @@ namespace Drivers::Audio::IntelHda {
 
     static void HandleInterrupt(uint8_t /*irq*/) {
         uint32_t intsts = Read32(REG_INTSTS);
+        bool bufferCompleted = false;
 
         // Handle stream interrupts (bits 0-29 correspond to stream descriptors)
         if (g_stream.Active) {
             uint8_t si = g_stream.StreamIndex;
             if (intsts & (1u << si)) {
                 uint8_t sts = ReadSD8(si, SD_STS);
+                if (sts & SD_STS_BCIS) bufferCompleted = true;
                 WriteSD8(si, SD_STS, sts);
             }
         }
@@ -858,6 +861,12 @@ namespace Drivers::Audio::IntelHda {
             uint8_t rirbSts = Read8(REG_RIRBSTS);
             Write8(REG_RIRBSTS, rirbSts);
         }
+
+        // Notify the mixer so it can refill the DMA ring with the next mix
+        // window. Done after clearing status bits so re-entry can't latch.
+        if (bufferCompleted) {
+            Mixer::OnHdaBufferComplete();
+        }
     }
 
     // =========================================================================