add depth configuration parity with the reference driver

parse_depth_mode returned NEURAL for any unrecognised string, so a typo
silently changed depth quality, and NEURAL_PLUS and NEURAL_LIGHT could not be
selected at all. All six modes are now reachable and an unknown name exits
non-zero listing the accepted values.

Parsing moves into Config::from_env() and main reads the configuration before
init_dora_node(), so a bad value fails with its own message instead of after
the node has registered with the dataflow.

Add ZED_CONFIDENCE_THRESHOLD (60) and ZED_TEXTURE_CONFIDENCE_THRESHOLD (100),
which were never set, and change the defaults to 1080 / 200 mm / 600 mm to
match the reference driver perception was tuned against. The resolved settings
are logged at startup.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y7g2cBJ5e3r15ZbJ9WZn8c

AGENTS.md

@@ -37,7 +37,7 @@ Camera behavior is configured entirely through environment variables (see README
 
 - **`src/util/env.h`** — Shared inline env-variable parsing helpers (`get_env_int`, `get_env_str`, `get_env_bool`, `get_env_float`).
 - **`src/zed/camera.h`** — `zed::Config`, `zed::Calibration`, and `zed::Camera` class. Camera wraps the ZED SDK lifecycle: open (with retry loop), warmup, grab (image + depth + point cloud), calibration, device timestamp, and close. Exposes `handle()` for engine access.
-- **`src/zed/camera.cc`** — Implementation. SDK enum parsers live in an anonymous namespace.
+- **`src/zed/camera.cc`** — Implementation. SDK enum parsers live in an anonymous namespace. `parse_depth_mode` runs in `Config::from_env()`, not in the constructor, so an unrecognised `ZED_DEPTH_MODE` exits before the node joins the dataflow rather than falling back to a default.
 - **`src/main.cc`** — Dora event loop. Parses `ZED_PC_MODE` (`FULL`/`HALF`) once before the loop. On any input event (intended to be driven by a tick timer; the id is not inspected): calls `camera.grab()`, then sends `image_bgr`, `depth`, `point_cloud` and `camera_info`. `pack_depth` copies the depth map into a tightly packed `[H, W]` float buffer (sl::Mat rows can be padded) and clears `inf`/`nan` to `0`. `set_intrinsics` and `set_frame_stamps` stamp every output of a frame with the same intrinsics, `frame_id` and the two timestamps (`device_timestamp_ns`, `host_timestamp_ns`; both Unix-epoch nanoseconds). Point cloud output varies by mode: `FULL` sends the raw `sl::Mat` pointer (no copy); `HALF` downsamples by 2 in each dimension. Handles reconnection on grab failure.
 - **`DoraTargets.cmake`** — Handles building or fetching dora-rs and generating the CXX bridge files. Two paths: local (`DORA_ROOT_DIR`) or git clone. Produces `dora_node_api_cxx` library and the `node_bridge.cc` glue.
 - **`scripts/build.sh`** — Configure/compile/install in one shell-free-callable step. Referenced by `dataflow.yml`, the `Dockerfile` and the README.