rebase: Phase B — trivial files for the v0.6.0 base

Build-system, config, usb, and CI wiring on top of upstream's
v0.6.0-hotfix tree. Build will still fail until Phase C+D land bt.h
accessors that oled.cpp references; that's expected mid-rebase.

CMakeLists.txt: add src/oled.cpp + src/slots.cpp to add_executable,
link hardware_spi, restore OUTPUT_NAME ds5-bridge-oled.

src/config.h: append the 4 OLED Edition Config_body fields
(current_slot + auto_haptics_enable/gain/lowpass). Preserves
upstream's field order for the first 8 fields.

src/config.cpp:
- speaker_volume validity default -100 dB → 0 dB (footgun fix)
- 4 new validity guards for the appended fields with sensible
  defaults (Fallback / 100 % / 160 Hz / slot 0)
- config_default() impl (was declared in upstream's config.h since
  v0.5.4 but never defined; the OLED Edition's "Reset to defaults"
  Settings item calls it)

src/usb.cpp: drop the UAC1 SET_CUR Volume → flash-config sync that
let PipeWire/Pulse silently override the user's saved Spk Vol on
every device reconnect. Borrowed from loteran/DS5Dongle commit
03fa1e4.

src/usb_descriptors.cpp: restore iSerialNumber = STRID_SERIAL.
Upstream's commit e79c762 zeroed it to work around SpecialK (#32),
but that broke Windows device identity (#100) — users lost
per-device volume / app preferences when moving USB ports. The
OLED Edition prioritizes Windows device-identity stability for
the broader user base over SpecialK compat for a narrower one.

.github/workflows/{build,release}.yml: artifact filenames use
ds5-bridge-oled.uf2 (and -debug / -picow variants) per the
OUTPUT_NAME rebrand.

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

src/config.h

@@ -17,6 +17,12 @@ struct __attribute__((packed)) Config_body {
     uint8_t polling_rate_mode; // 0: 250Hz, 1: 500Hz, 2: real-time
     uint8_t audio_buffer_length; // [16,128]
     uint8_t controller_mode; // 0: DS5, 1: DSE, 2: Auto
+    uint8_t current_slot;    // [0..3] active multi-pairing slot (OLED Edition Phase G)
+    // Audio Auto Haptics — derive haptic feedback from speaker audio for games that
+    // send no per-frame native haptic data. DSP borrowed from loteran/DS5Dongle 5d6bc2f.
+    uint8_t auto_haptics_enable;  // 0=Off, 1=Fallback (default), 2=Mix, 3=Replace
+    uint8_t auto_haptics_gain;    // [0,200] percent, default 100
+    uint8_t auto_haptics_lowpass; // 0=80Hz, 1=160Hz (default), 2=250Hz, 3=400Hz
 };
 
 struct __attribute__((packed)) Config {