feat(tool): add offline map merge via cross-map loop closure

[junlinp]

Summary

• Add tool/merge_maps.py to merge two TinyNav map directories into one output map.
• Find cross-map loop closure with saved DINO embeddings, verify candidates with SuperPoint + LightGlue, estimate alignment via PnP, and optimize the map-B-to-map-A transform with the pose graph solver.
• Add scripts/run_map_merge.sh launcher with CLI flags for map paths, thresholds, and device/runtime environment setup.

Test plan

• Run bash scripts/run_map_merge.sh --map-a <map_a> --map-b <map_b> --output <merged> --overwrite on two overlapping maps with valid embeddings/features.
• Confirm output contains merged poses.npy, occupancy_grid.npy, sdf_map.npy, and merge_report.json.
• Verify merged poses and occupancy look consistent in RViz or existing map visualization tooling.

Made with Cursor

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (259.3 files/s, 38431.7 lines/s)

Language	files	blank	comment	code
Python	13	619	262	3462
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	16	49	18	367
Dockerfile	1	31	32	203
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	43	948	371	5055

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (253.3 files/s, 37541.9 lines/s)

Language	files	blank	comment	code
Python	13	619	262	3462
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	16	49	18	367
Dockerfile	1	31	32	203
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	43	948	371	5055

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.13 s (320.5 files/s, 47511.1 lines/s)

Language	files	blank	comment	code
Python	13	619	262	3462
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	16	49	18	367
Dockerfile	1	31	32	203
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	43	948	371	5055