Round image: drop dead ifupdown config, give secubox sudo, fix misleading OTG comment (closes #139) (#143)

* fix(round): remove dead ifupdown config + secubox sudo + clarify gadget IP comment (closes #139)

Three small cleanups against the round image, all triggered by the
follow-up to PR #137's OTG bench:

1. Drop `remote-ui/round/files/etc/network/interfaces.d/usb0` — the
   stanza configured `usb0` via `ifupdown`, but `ifupdown` is not in
   the apt list, `networking.service` is inactive, and the actual IP
   binding happens in `secubox-otg-gadget.sh` (which configures `usb1`
   programmatically with `ip addr add`). Keeping the file on disk
   misleads diagnostics — it cost a round trip during the 2026-05-15
   bench when I assumed `usb0`/10.55.0.2 must be where the IP would
   land. Deleting it.

2. Add `sudo` to the `secubox` user's group list in
   `build-eye-remote-image.sh`. Without it, ACM serial console
   recovery is impossible — the user can log in but can't fix
   anything. The round previously needed `pi/raspberry` (which the
   build script does not provision) as a fallback; now `secubox` can
   recover networking from the only path that survives a broken IP
   link.

3. Rewrite the misleading comment block in `secubox-otg-gadget.sh`
   about which kernel interface name belongs to which gadget function.
   The legacy comment claimed `usb1 = ECM` and tied the binding choice
   to "Linux uses cdc_ether"; in reality both RNDIS and ECM share the
   same host_addr so the host can reach 10.55.0.2 via either function
   (verified on Pop!_OS 22.04 host: ping succeeded with 10.55.0.1
   bound on the host's RNDIS leg). Comment now states the actual
   contract: bind on `usb1` (the second-registered network function),
   independent of which transport carries the packets.

Test plan
---------

- [ ] Rebuild the round image and flash to Pi Zero W 1st gen.
- [ ] Verify boot still reaches OFFLINE-mode radar on the HyperPixel.
- [ ] `id secubox` on the booted device shows `sudo` in groups.
- [ ] `ls /etc/network/interfaces.d/usb0` returns "no such file".
- [ ] `systemctl is-active secubox-otg-gadget` returns `active`.
- [ ] Host ping 10.55.0.2 succeeds (regression check — the comment
      rewrite is documentation-only, must not change behaviour).

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

* fix(round): also drop inline heredoc that recreates dead ifupdown stanza (ref #139)

The previous commit deleted remote-ui/round/files/etc/network/interfaces.d/usb0
but missed that build-eye-remote-image.sh writes the same file inline at
build time via heredoc. Without removing that block too, the dead config
keeps shipping to the rootfs.

Verified on the just-rebuilt image: file still present after first
attempt at the fix. With both source-tree deletion AND the heredoc gone,
the config never lands.

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

---------

Co-authored-by: CyberMind-FR <gandalf@Gk2.net>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

remote-ui/common/shell/secubox-otg-gadget.sh

@@ -284,9 +284,14 @@ gadget_start() {
     log "Activation sur UDC: ${udc}"
     echo "$udc" > UDC
 
-    # Attendre que l'interface usb1 (ECM) apparaisse
-    # Note: Le gadget composite crée usb0 (RNDIS/Windows) et usb1 (ECM/Linux-Mac)
-    # On configure usb1 car les hôtes Linux utilisent le driver cdc_ether (ECM)
+    # Attendre que la deuxième interface réseau du gadget composé
+    # apparaisse côté kernel. Le composé crée rndis.usb0 puis ecm.usb0
+    # (dans cet ordre, cf. liens configfs ci-dessus) — le kernel les
+    # enregistre comme /sys/class/net/usb0 et /sys/class/net/usb1.
+    # Côté hôte, RNDIS et ECM partagent le même host_addr donc l'ARP
+    # remonte sur n'importe laquelle des deux interfaces UP du host;
+    # binder /usb1 ici suffit pour rendre 10.55.0.2 joignable depuis
+    # 10.55.0.1, peu importe le canal physique sélectionné par l'hôte.
     local retry=0
     while [[ ! -d /sys/class/net/usb1 ]] && [[ $retry -lt 10 ]]; do
         sleep 0.5
@@ -294,9 +299,9 @@ gadget_start() {
     done
 
     if [[ -d /sys/class/net/usb1 ]]; then
-        log "Interface usb1 (ECM) créée"
+        log "Interface usb1 (deuxième fonction réseau du gadget) créée"
 
-        # Configurer l'IP sur usb1 uniquement (évite le routage asymétrique)
+        # Configurer l'IP sur usb1 uniquement (évite le routage asymétrique).
         ip addr flush dev usb1 2>/dev/null || true
         ip addr add "${OTG_NETWORK_DEV}/30" dev usb1
         ip link set usb1 up

remote-ui/round/build-eye-remote-image.sh

@@ -704,15 +704,12 @@ ln -sf /etc/systemd/system/secubox-serial-console.service \
 # NOTE: fb-dashboard is DEPRECATED - use fallback-display instead
 # The old dashboard is kept for reference but NOT enabled by default
 
-# Network config for usb0
-mkdir -p "$ROOT_MNT/etc/network/interfaces.d"
-cat > "$ROOT_MNT/etc/network/interfaces.d/usb0" << 'EOF'
-allow-hotplug usb0
-iface usb0 inet static
-    address 10.55.0.2
-    netmask 255.255.255.252
-    gateway 10.55.0.1
-EOF
+# IP binding for the gadget's usb1 interface is handled by
+# /usr/local/sbin/secubox-otg-gadget.sh (the same script that composes
+# the configfs gadget). The legacy /etc/network/interfaces.d/usb0
+# stanza was removed (closes #139) — it required `ifupdown` which the
+# image never installed, so it never did anything except confuse
+# diagnostics.
 
 # USB network script (handles both usb0 and usb1 - ECM may create either)
 mkdir -p "$ROOT_MNT/usr/local/bin"
@@ -787,8 +784,9 @@ if ! id secubox &>/dev/null; then
     echo "secubox:secubox2026" | chpasswd
 fi
 
-# Add to groups
-usermod -aG video,input,gpio,i2c,spi,audio secubox 2>/dev/null || true
+# Add to groups. `sudo` lets the kiosk user manually recover networking
+# from the ACM serial console (e.g. when /dev/ttyACM0 is the only path in).
+usermod -aG sudo,video,input,gpio,i2c,spi,audio secubox 2>/dev/null || true
 
 # Enable lightdm and nginx
 systemctl enable lightdm 2>/dev/null || true

remote-ui/round/files/etc/network/interfaces.d/usb0

@@ -1,5 +0,0 @@
-allow-hotplug usb0
-iface usb0 inet static
-    address 10.55.0.2
-    netmask 255.255.255.252
-    gateway 10.55.0.1