fix(camera): resolve RCE acquisition path against data root for manifest

[larsrollik]

Problem

On acquisition machines using the RCE camera backend, every session logged a FileNotFoundError traceback and silently failed to record the camera acquisition in session_manifest.yaml.

The RCE adapter receives acquisition_path relative to the data root (the remote conductor needs it relative), but reused that same relative value to write the local session_manifest.yaml. The write resolved against the process CWD, which on most machines is not the data root, so the directory did not exist and the manifest write raised FileNotFoundError. It was caught as best-effort bookkeeping (logged as a WARNING, acquisition continued), so it surfaced as noise plus a missing camera peer entry.

Only RCE setups were affected: FLIR setups pass an absolute acqdir, and no-camera setups skip registration entirely.

Fix

• Resolve acquisition_path against output_dir (the data root) before registering and finalizing the camera peer, leaving the relative path untouched for the remote conductor.
• Backward compatible: joining the data root with an already-absolute path returns the absolute path unchanged.

Tests

• Added a regression test exercising the real relative-path caller usage.
• 4 passing in test_camera_peer_registration.

Version bump: patch.