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/build_sdk.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+# Makes sure an OrbbecSDK v2 build exists for THIS platform, and prints where it
+# is as OB_SDK_ROOT=... / OB_SDK_BUILD=... / OB_SDK_GENERATED=... for build_server.sh.
+#
+# Never ships a prebuilt binary between Jetsons: CUDA and glibc differ by
+# generation, so the SDK is built from source on the machine that will run it.
+# The heavy artifact stays out of git.
+#
+# Order of preference:
+#   1. An existing build pointed to by $OB_SDK_ROOT — reused as-is. This is what
+#      keeps a working node (the Nano already has one) untouched.
+#   2. A build at one of the known locations, likewise reused.
+#   3. A fresh clone + build. On a new JetPack this is the step to watch; if it
+#      fails, build the SDK by hand once and re-run install.sh with OB_SDK_ROOT set.
+set -euo pipefail
+
+here=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+eval "$("$here/detect_platform.sh")"
+
+# The official v2 source. Pinned loosely: a caller can override both to match a
+# tag known to build on their JetPack.
+SDK_REPO="${OB_SDK_REPO:-https://github.com/orbbec/OrbbecSDK_v2.git}"
+SDK_REF="${OB_SDK_REF:-main}"
+
+find_build() {
+    local root="$1"
+    [[ -f "$root/include/libobsensor/ObSensor.hpp" ]] || return 1
+    local b
+    b=$(ls -d "$root"/build/linux_* 2>/dev/null | head -1)
+    [[ -z "$b" ]] && b="$root/build"
+    [[ -f "$b/lib/libOrbbecSDK.so" ]] || return 1
+    echo "$b"
+}
+
+emit() {
+    local root="$1" build="$2"
+    echo "OB_SDK_ROOT=$root"
+    echo "OB_SDK_BUILD=$build"
+    echo "OB_SDK_GENERATED=$root/build/src/generated"
+}
+
+# 1 & 2: reuse whatever is already built.
+for candidate in "${OB_SDK_ROOT:-}" \
+                 "$HOME/OrbbecSDK_v2" \
+                 "$HOME/OrbbecSDK_v2_jetson"; do
+    [[ -z "$candidate" ]] && continue
+    if b=$(find_build "$candidate" 2>/dev/null); then
+        echo ">> SDK deja bati, reutilise: $candidate" >&2
+        emit "$candidate" "$b"
+        exit 0
+    fi
+done
+
+# 3: clone + build from source.
+root="${OB_SDK_ROOT:-$HOME/OrbbecSDK_v2}"
+echo ">> Aucun SDK bati — clone et compilation (JetPack ${JETPACK}, ${SOC})" >&2
+echo ">> ${SDK_REPO} @ ${SDK_REF} -> ${root}" >&2
+
+if [[ ! -d "$root/.git" ]]; then
+    git clone --depth 1 --branch "$SDK_REF" "$SDK_REPO" "$root" >&2
+fi
+
+build="$root/build/linux_$(uname -m)"
+mkdir -p "$build"
+(
+    cd "$build"
+    # -DOB_BUILD_EXAMPLES=ON gives the k4a recorder sample used as recorder_bin.
+    cmake ../.. -DCMAKE_BUILD_TYPE=Release -DOB_BUILD_EXAMPLES=ON >&2
+    make -j"$(nproc)" >&2
+)
+
+if ! b=$(find_build "$root" 2>/dev/null); then
+    cat >&2 <<EOF
+
+!! La compilation du SDK ne s'est pas terminee comme attendu.
+!! Bâtis-le une fois a la main, puis relance install.sh en pointant dessus :
+!!     OB_SDK_ROOT=<chemin> ./install.sh
+EOF
+    exit 1
+fi
+echo ">> SDK bati: $b" >&2
+emit "$root" "$b"