Fix "Tab says denied even though I'm in range of beta": root cause is the
race between the 20 Hz move-stream sampler and the target-select POST. A
Tab press right after the capsule stops can be validated against the
server's last sampled position, which trails the visible capsule by
several meters.
Client-side fixes (server contract unchanged):
- TargetSelectionClient.set_freshness_kick(authority, player): before each
POST /target/select, submit a move-stream with the current player
position so the server's stored snapshot is as fresh as possible when
the range check runs. Wired in main.gd; optional so tests without the
wiring still pass (regression-covered).
- PlayerPositionLabel now shows a "srv: (x,y,z) Δ=<d>m age=<ms>" line
populated from PositionAuthorityClient.authoritative_ack, so any
residual client/server divergence is visible in the HUD and future
reports can point at it directly.
- Two new tests: select POST kicks exactly one freshness stream with the
current player position before POSTing, and the kick is a no-op when
the wiring is absent.
Docs: plan Decision 5, review follow-up #2, manual QA section 5 and
section 1, and client README updated to describe the new behaviors.