Portable Ithaca capture node: one install for every Jetson

Extract the install that was applied by hand to the Jetson Nano into a single
checkout that builds itself for whatever Jetson it lands on.

The two nodes on the rig share no JetPack — tegra210 caps at 4, tegra234 needs
5+ — so nothing binary is portable between them. The source and the procedure
are: install.sh detects the platform (L4T / JetPack / SoC), installs deps,
builds the OrbbecSDK and the preview server from source locally, and generates
a per-user config and systemd unit. The tested bridge.py ships verbatim; all
machine-specific paths live in the generated config, so it stays unmodified —
its one hardcoded path is made home-relative.

The retired GStreamer/RTSP target is dropped: the direct route encodes no video.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

scripts/detect_platform.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# Prints the facts every other script branches on, one KEY=value per line, so a
+# caller can `eval "$(detect_platform.sh)"`.
+#
+# The point of the whole repo is that these differ between Jetsons and nothing is
+# assumed: the original Nano is tegra210 on L4T R32 (JetPack 4, Ubuntu 18.04,
+# CUDA 10.2), an Orin is tegra234 on R35/R36 (JetPack 5/6). One install procedure,
+# values read here, binaries built locally to match.
+set -euo pipefail
+
+# L4T release, e.g. "32.7.1" or "36.4.3". Two sources; the file is the reliable
+# one on every generation, the package is the cross-check.
+l4t=""
+if [[ -f /etc/nv_tegra_release ]]; then
+    # "# R32 (release), REVISION: 7.1, ..." -> 32.7.1
+    rel=$(sed -n 's/^# R\([0-9]*\).*REVISION: \([0-9.]*\).*/\1.\2/p' /etc/nv_tegra_release)
+    l4t="$rel"
+fi
+if [[ -z "$l4t" ]] && command -v dpkg-query >/dev/null 2>&1; then
+    l4t=$(dpkg-query --showformat='${Version}' -W nvidia-l4t-core 2>/dev/null \
+          | sed 's/-.*//') || true
+fi
+
+major="${l4t%%.*}"
+
+# SoC family, from the device tree — the ground truth for what can run here.
+soc="unknown"
+if [[ -r /proc/device-tree/compatible ]]; then
+    comp=$(tr '\0' '\n' < /proc/device-tree/compatible)
+    case "$comp" in
+        *tegra210*) soc="tegra210" ;;  # Nano, TX1
+        *tegra186*) soc="tegra186" ;;  # TX2
+        *tegra194*) soc="tegra194" ;;  # Xavier
+        *tegra234*) soc="tegra234" ;;  # Orin
+        *tegra264*) soc="tegra264" ;;  # Thor
+    esac
+fi
+
+model="unknown"
+[[ -r /proc/device-tree/model ]] && model=$(tr -d '\0' < /proc/device-tree/model)
+
+# JetPack generation follows from the L4T major, and it is what decides toolchain
+# and dependency names.
+case "$major" in
+    32) jetpack="4" ;;
+    35) jetpack="5" ;;
+    36) jetpack="6" ;;
+    38) jetpack="7" ;;
+    *)  jetpack="unknown" ;;
+esac
+
+echo "L4T=${l4t:-unknown}"
+echo "L4T_MAJOR=${major:-unknown}"
+echo "JETPACK=${jetpack}"
+echo "SOC=${soc}"
+echo "ARCH=$(uname -m)"
+echo "MODEL=${model}"