Enable in-container USB flashing + flash-re-bba-rb skill; find U7 EEPROM undersized

Devcontainer now grants libusb access to the FT2232H so iceprog (bitstream) and
pyftdi (FT2232H EEPROM) run inside the container:
- devcontainer.json: --privileged + /dev/bus/usb bind mount
- Dockerfile: sudo (NOPASSWD for vscode; USB nodes are root-owned), libusb-1.0-0,
  libftdi1-2, pyftdi

Add the flash-re-bba-rb skill documenting the procedure (bitstream via best swept
seed, optional EEPROM string, troubleshooting, guardrails) and
flash_ftdi_eeprom.py (pyftdi, backup-first, dry-run default) + ftdi_eeprom.conf
value spec.

Bring-up on the repaired V1 unit: bitstream flash VERIFY OK (iceprog
build/seed4/top.bin, capture 58.36 MHz). EEPROM product string CANNOT be
programmed on V1 — U7 is a 93LC46B (128 B), too small for the FT2232H, which
needs a 93LC56B (256 B); the 128 B chip mirrors and the config write fails
verify. This overturns the old REVIEW note "93LC46B = correct for FT2232H"
(that only checked ORG, not size). Board still works blank -> ROM defaults;
iceprog + UART unaffected. Documented in REVIEW.md + TODO.md (swap U7->93LC56B
for V2); flash_ftdi_eeprom.py detects the mirroring and refuses the write.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.devcontainer/Dockerfile

@@ -4,18 +4,24 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     ca-certificates \
     git \
     git-lfs \
+    sudo \
     python3 \
     python3-venv \
     python3-pip \
     yosys \
     nextpnr-ice40 \
     fpga-icestorm \
+    libusb-1.0-0 \
+    libftdi1-2 \
     nodejs npm \
     graphviz \
     poppler-utils \
     kicad \
     kicad-libraries \
     && rm -rf /var/lib/apt/lists/*
+# libusb-1.0-0 + libftdi1-2: USB backend for `iceprog` (FPGA flash) and `pyftdi`
+# (FT2232H EEPROM).  sudo: the /dev/bus/usb nodes are root-owned, so the vscode
+# user flashes via `sudo` (NOPASSWD, configured below).
 
 # Debian marks the system Python as externally-managed (PEP 668), so install
 # project deps into a venv. /opt/venv is first on PATH, so `python`/`pip` resolve
@@ -29,7 +35,12 @@ RUN npm install -g @anthropic-ai/claude-code
 COPY requirements.txt /tmp/requirements.txt
 RUN pip install --no-cache-dir -r /tmp/requirements.txt
 
-RUN useradd -m -u 1000 -s /bin/bash vscode
+# pyftdi: programs the FT2232H EEPROM (product string "re-BBA-rb") over libusb.
+RUN pip install --no-cache-dir pyftdi
+
+RUN useradd -m -u 1000 -s /bin/bash vscode \
+ && echo 'vscode ALL=(ALL) NOPASSWD:ALL' > /etc/sudoers.d/vscode \
+ && chmod 0440 /etc/sudoers.d/vscode
 
 USER vscode