rebase: Phase E — VU peaks, frame counters, Audio Auto Haptics

Build now compiles. audio.cpp on top of upstream's state_mgr-based
audio_loop adds three additive pieces:

1. VU peak meters for ch0/1 (spk_max) and ch2/3 (hap_max) tracked
   per-sample in the existing loop; written back to g_peak_spk /
   g_peak_hap after. Accessors decay 12.5% per read so the OLED
   VU bars fall back naturally over a few frames.

2. Monotonic byte-flow counters: g_usb_frames++ after tud_audio_read
   (the OLED Diagnostics screen + web emulator compute USB-aud/s
   and BT-0x32/s as delta over time). g_bt_packets++ after each
   0x36 bt_write.

3. Audio Auto Haptics DSP — 1-pole LP + envelope follower +
   modulation + soft-clip per loteran/DS5Dongle 5d6bc2f, with our
   added 4th "Fallback" mode that fires only after the game's
   native haptic path has been silent for ~1 s (NATIVE_SILENT_TIMEOUT
   = 100 audio_loop calls). Preserves native HD haptics (Spider-Man
   Remastered) while filling in for games that send no haptic data
   (Ghost of Tsushima). Modes: 0=Off, 1=Fallback (default), 2=Mix,
   3=Replace.

Crucially the state_mgr-based state_set(pkt+13, 63) call is left
untouched — that's upstream's correct replacement for our prior
state_data restore hack, and it's load-bearing for speaker output.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/audio.h

@@ -5,9 +5,21 @@
 #ifndef DS5_BRIDGE_AUDIO_H
 #define DS5_BRIDGE_AUDIO_H
 
+#include <cstdint>
+
 void audio_init();
 void audio_loop();
 void core1_entry();
 void set_headset(bool state);
 
+// Accessors used by the optional OLED add-on (diag + VU meter screens).
+uint32_t audio_fifo_drops();
+uint32_t opus_fifo_drops();
+uint8_t  audio_peak_speaker();   // 0..255, decays on read
+uint8_t  audio_peak_haptic();    // 0..255, decays on read
+
+// Byte-flow counters for the Diagnostics screen + web emulator.
+uint32_t audio_usb_frames();
+uint32_t audio_bt_packets();
+
 #endif //DS5_BRIDGE_AUDIO_H