Take the stereo calibration from DIVE instead of a global directory

[mattdawkins]

Problem

The measurement and ifremer stereo pipes pointed their calibration at a global:input_cameras_directory defaulting to /home/<user>/Desktop/..., exposed as a DIVE folder picker.

That picker was a no-op. $CONFIG{} expands at parse time with backward references only, while -s blocks are appended last, so overriding the global never reached the consuming process — runs silently used the hardcoded path.

Changes

• Name the consuming process keys directly and declare them in a # Calibration Keys: header (needs Let a pipe declare which config keys receive the calibration file Kitware/dive#1814)
• Route ocv_stereo_disparity and the ifremer ocv_pair_stereo_* processes through read_stereo_rig, which already handles both files and OpenCV directories, so they accept .json/.yml/.npz/.mat — DIVE hands down a single file, but these only ever read a directory of intrinsics.yml + extrinsics.yml
• Rename their cameras_directory config to calibration_file, matching every other camera file parameter
• Those formats carry no rectification transforms, so stereoRectify now derives them on the first frame, where an image size is finally known
• Image-producing pipes default their output directory to .

Verification

• kwiver pipe-config confirms -s now reaches depth_map:computer:ocv_stereo_disparity:calibration_file, and that the output template bakes to ./depth_map%06d.png
• viame_opencv and viame_processes_opencv build and link clean
• DIVE's discovery resolves the expected keys for all six calibration-requiring pipes

Note

calibration_params.conf still has /home/<user>/... paths for video_filename / tracks_left|right — those are example inputs DIVE overrides per-run, left as documentation.