feat(mapping): add BoW loop-closure mode for map and build-map nodes

[junlinp]

Summary

• add BoW loop-closure runtime mode to build_map_node.py and map_node.py
• switch to ORB extractor + BF matcher + dummy embedding engine when mode is bow
• route loop candidate search through LoopClosure API in both nodes
• make map relocalization use persistent prebuilt LoopClosure index (query-only)
• add default DBoW3 vocabulary path (/tinynav/docs/Vocabulary/ORBvoc.txt)
• fix pydbow3 vocabulary load return-value handling in DBoW3Engine
• track docs/Vocabulary/ORBvoc.txt via Git LFS

Notes

• BoW mode is enabled by either --loop-closure-use-bow or --loop-closure-mode bow.
• Vocabulary file must exist at runtime or be overridden with --dbow3-vocabulary-path.

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (252.3 files/s, 39608.0 lines/s)

Language	files	blank	comment	code
Python	13	666	289	3876
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
Text	1	0	0	3
--------	--------	--------	--------	--------
SUM:	43	987	387	5376

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (250.8 files/s, 39857.9 lines/s)

Language	files	blank	comment	code
Python	13	668	293	3955
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
Text	1	0	0	3
--------	--------	--------	--------	--------
SUM:	43	989	391	5455

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.18 s (252.7 files/s, 38256.0 lines/s)

Language	files	blank	comment	code
Python	13	667	296	3961
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	18	64	15	360
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
Text	1	0	0	3
--------	--------	--------	--------	--------
SUM:	46	1011	402	5550

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (267.2 files/s, 40847.0 lines/s)

Language	files	blank	comment	code
Python	13	667	296	3961
Markdown	4	155	6	426
Bourne Shell	18	77	16	416
C++	4	60	38	409
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
Text	1	0	0	3
--------	--------	--------	--------	--------
SUM:	46	1024	403	5606