fix: marking the same child twice should leave you with one child

[ralyodio]

Reported from real use: "it created each focal selection into a duplicate player and in the end it just uses one selection not all of them."

Exactly right. The live project had 8 athletes, 7 of them "My athlete", created inside three minutes, one fragment each:

ath_751aef7a 'My athlete'  focal=True   14:14:57
ath_599b1f9a 'Fred' #14 Triton (white)  14:10:09
ath_79c5eda0 'My athlete'               14:12:35
ath_52123626 'My athlete'               14:12:51
ath_f4d669e6 'My athlete'               14:13:21
ath_deb93569 'My athlete'               14:13:58
ath_c5321e91 'My athlete'               14:14:19
ath_1b035ae5 'My athlete'               14:14:46

Why

new in the identify route means "I have not told you who this is", and it was calling addAthlete unconditionally. The client sends new whenever its own athlete list hasn't loaded — which is every click made faster than a page reload. So the faster you worked, the more duplicates you got, and each new athlete was made focal in turn. Scoring reads the focal flag, so all that careful selecting collapsed to the last click.

The fix

Two halves:

1. new prefers the athlete already being followed and only creates one when there genuinely is none. Identifying is still the one step that can't be skipped, so first-run behaviour is unchanged.

2. A new call adds; a named call replaces. A caller that said new didn't know who this was and can't have sent the fragments already bound, so replacing silently discarded every earlier pick. The picker holds the whole selection and names the athlete, so it still replaces — that's what makes unticking a crop work.

Test

apps/web/src/identifytwice.test.ts drives the real route through registerActions, simulating clicks with no loaded client state.

• before: 3 clicks → 3 athletes (expected […] to have a length of 1 but got 3)
• after: 1 athlete holding all 3 fragments, focal

574 tests pass, 8 skipped. Lint and build clean.

Not in this PR

Also raised in the same report, and worth separate changes: jersey/team shown in the picker so "#14 white" is distinguishable from "#14 black"; ball detection recall; and replacing the full-page reloads with live updates and progress so it's clear when to wait and when to act.

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