Implement multi-scan assembly from rtabmap-reprocess reference

[github-actions]

Need to port logic from RTABMap's reprocess tool to assemble multiple scans:
Reference: https://github.com/introlab/rtabmap/blob/master/tools/Reprocess/main.cpp
Key steps:

1. Load multiple .db files and extract pose graphs
2. Perform global registration/alignment between scans
3. Set default parameters optimized for building interiors (rux use case)
4. Merge point clouds and update node links in output database
5. Run graph optimization to refine alignment
   This unblocks the multi-scan workflow for large building projects

Line: 67

ReUseX/apps/rux/src/assemble.cpp

Lines 64 to 74 in f6e1667

	spdlog::debug("Input files: {}", fmt::join(input_files, ", "));
	// TODO: Implement multi-scan assembly from rtabmap-reprocess reference
	// category=CLI estimate=1w
	// Need to port logic from RTABMap's reprocess tool to assemble multiple scans:
	// Reference: https://github.com/introlab/rtabmap/blob/master/tools/Reprocess/main.cpp
	// Key steps:
	// 1. Load multiple .db files and extract pose graphs
	// 2. Perform global registration/alignment between scans
	// 3. Set default parameters optimized for building interiors (rux use case)