feat(osmAG): add standalone C++ build, AlphaRemoval noise cleaning, CGAL safety checks, and visual stage export

[abdulrahimzulfiqar]

Summary of Changes

This Pull Request resolves standalone build errors, fixes fatal CGAL precondition crashes on noisy maps, restores missing furniture noise pre-processing from the 2019 Area Graph paper, and adds automated visual stage image export.

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1. Standalone Build & Dependency Resolution (ag_osm_generator & osmAG)

• Resolved CMake Dependencies: Added missing CMake configuration for Qt5 (Qt5::Widgets, Qt5::Gui), CGAL, OpenCV, Eigen3, and PCL.
• Embedded C++ Source Tree: Fixed missing headers and source files in ag_osm_generator to enable clean standalone C++ building without legacy ROS 1 catkin dependencies.

2. Restored performAlphaRemoval Noise Cleaning

• Restored Pre-Processing Step: In ag_osm_generator/src/AreaGenerate.cpp, added #include "cgal/AlphaShapeRemoval.h" and invoked performAlphaRemoval().
• Furniture Clutter Filtering: Automatically strips 3D LiDAR furniture scans and trash bin noise specks from clean.png prior to Voronoi site generation, reducing fragmented 48-polygon decompositions into clean room boundaries.

3. CGAL Assertion & Crash Safeguards (is_simple())

• Prevented CGAL Precondition Crashes: In ag_osm_generator/src/cgal/CgalVoronoi.cpp, wrapped calls to polygon.bounded_side(p) with polygon.is_simple() checks.
• Self-Intersecting Loop Protection: Safely skips non-simple contour loops on complex maps instead of throwing uncaught CGAL::Precondition_exception: is_simple() abort errors.

4. Automated Visual Stage Image Export

• Room Graph (roomGraph.png): Updated ag_osm_generator/src/Area_osm.cpp to automatically save color-coded Voronoi room segmentation maps with red topological room-center nodes.
• Stage 2 Room Submaps: Updated osmAG/src/data_load_save.cpp to iterate through all leaf area cells (InitOccupancyMap_Area) and export 2D Occupancy Grid Submap images (<map_name>_stage2_room_submap_<1..N>.png).
• Stage 3 & Stage 4 Vector Rendering: Updated osmAG/src/visualization.cpp with auto-scaled canvas math to render prominent magenta global A* path trajectories, start/goal markers, and passage graph overlays.

5. Flexible Command-Line Output Path

• Custom Output Destination: Updated ag_osm_generator/test/test_osm_generation.cpp to accept an optional 10th argument (argv[10]) specifying the custom target .osm XML path.

6. Documentation & Build Guides

• Comprehensive Layman Guide: Completely updated root README.md and ag_osm_generator/ReadMe with system architecture diagrams, macOS/Ubuntu prerequisites, argument reference tables (explaining effective door width $W = \text{door} + 0.1\text{m}$), and copy-paste commands.

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Verification & Testing

• Tested on clean custom maps (big_map_7_cleaned.png: 8 leaf submaps, 4 rooms, 74 A* waypoints).
• Tested on noisy benchmark maps with furniture clutter (Freiburg79_scan_furnitures_trashbins.png: 44 leaf submaps, 21 passages, 319 A* waypoints over 32.98m).