Fix boot-to-login: override pcid-spawner to oneshot_async, add U3 input producers, Intel HDA phases A-D

- Override 00_pcid-spawner.service to oneshot_async in redbear-legacy-base.toml:
  rootfs phase no longer blocks on PCI driver init; getty/login starts immediately.
  Confirmed working on both QEMU and bare metal (redbear-live-mini).
- Clean up 00_base legacy script: remove dead notify ipcd/ptyd calls, keep sudo --daemon.
- Add U3 named input producers: inputd supports per-device named producers with
  fan-out to both device-specific consumers and legacy VT consumers. Migrate ps2d
  and usbhidd to InputProducer trait. RESERVED_DEVICE_NAMES deduplicated.
- Add Intel HDA audio driver phases A-D: ihdad error handling (37 fixes), audio
  quirks, codec path enumeration, mixer/volume control.
- Add init service start/readiness logging (always visible, not debug-gated).
- Update BOOT-PROCESS-ASSESSMENT.md: Phase 6 complete, boot procedure documented,
  validation matrix updated with confirmed boot status.
- Update USB-IMPLEMENTATION-PLAN.md and INPUT-SCHEME-ENHANCEMENT.md for U2/U3 status.

local/recipes/system/redbear-quirks/source/quirks.d/15-audio.toml

@@ -0,0 +1,44 @@
+# Audio controller and codec quirks.
+# These apply to HDA controllers and codec devices.
+
+# Intel ICH8 HDA — force EAPD on outputs
+[[pci_quirk]]
+vendor = 0x8086
+device = 0x284b
+flags = ["audio_force_eapd"]
+
+# Intel ICH9 HDA (QEMU) — use immediate command interface
+[[pci_quirk]]
+vendor = 0x8086
+device = 0x293e
+flags = ["audio_single_cmd"]
+
+# Intel 6-series PCH HDA — position fix LPIB
+[[pci_quirk]]
+vendor = 0x8086
+device = 0x1c20
+flags = ["audio_position_fix_lpib"]
+
+# Intel 7-series PCH HDA — position fix LPIB
+[[pci_quirk]]
+vendor = 0x8086
+device = 0x1e20
+flags = ["audio_position_fix_lpib"]
+
+# Intel Sunrise Point HDA — position fix LPIB
+[[pci_quirk]]
+vendor = 0x8086
+device = 0xa170
+flags = ["audio_position_fix_lpib"]
+
+# Intel Cannon Point HDA — position fix LPIB
+[[pci_quirk]]
+vendor = 0x8086
+device = 0x9dc8
+flags = ["audio_position_fix_lpib"]
+
+# AMD FCH HDA — single command fallback
+[[pci_quirk]]
+vendor = 0x1022
+device = 0x1457
+flags = ["audio_single_cmd"]