feat(nav): support map handoff flow

[xiaolefang-dm]

Summary

• add map/nav-flow handoff support from one map to another after reaching configured POIs
• support handoff rules keyed by POI name or ID, with legacy index fallback
• add a short nav_done grace window to avoid races when final nav_progress and nav_done arrive close together

Testing

• Not run (draft PR for discussion/review)

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.19 s (221.9 files/s, 35298.7 lines/s)

Language	files	blank	comment	code
Python	13	673	306	3787
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	32	204
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	49
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	994	406	5280

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.18 s (232.8 files/s, 37364.4 lines/s)

Language	files	blank	comment	code
Python	13	680	305	3843
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	32	204
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	49
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	1001	405	5336