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>

.gitignore

@@ -0,0 +1,16 @@
+# Generated for the local user by install.sh — never committed, it holds this
+# machine's paths.
+bridge/config.json
+
+# Build outputs.
+server/build/
+
+# The runtime state the bridge writes beside itself.
+bridge/cam_settings.json
+bridge/cam_index.json
+bridge/stream_map.txt
+bridge/*.log
+
+# Python.
+__pycache__/
+*.pyc