routePlanProvider's AsyncLoading state collapsed with "route doesn't exist"
via .valueOrNull, so a brand-new route's screen briefly rendered "This route
no longer exists." with no FlutterMap in the tree before the DB stream's
first emission arrived. Add a hasValue guard mirroring waypointsAsync's
existing pattern, and replace the route planner's hardcoded initialZoom of
14 with FB-01's ambientZoom constant for street-level parity with the rest
of the app.
Turns docs/FEEDBACK.md into five self-contained tickets, each grounded in
exact current code and a concrete implementation approach, so they can be
handed to independent subagents with no prior context.
