wc-matchday-timing — kickoff spread, bench order, manual-sub triggers

Implements the BB6 matchday-spread constraint in footballfantasy/context/frameworks/building-blocks.md and the manual-substitution rule in context/league-config.md. This skill owns the structural plumbing under the two point-winning levers: the captain ladder (owned by wc-captain-ladder) and manual subs. Neither lever works on a squad whose players all kick off in the same window — there is nothing to switch to, nobody left to promote. This skill measures whether the build has that material, and if so, lays out the bench and the triggers that turn it into points.

The edge is concrete: league-config.md states an active manager working the captain ladder + manual subs gains ~20–40 points per round over a set-and-forget manager. That edge is only available when the squad is spread across the round's match days. This skill protects that availability.

One hard fact this skill is built around: a manual sub only works if the bench player has not yet kicked off. Once a match has started, that player's score is locked — promotable players are exactly the ones whose kickoff is still in the future. So bench order is primarily a kickoff-time problem, and only secondarily a points problem. Order by kickoff first; break ties by xEV.

Workflow

- [ ] 1. Load the round's match-day calendar (which days, kickoff times UTC) — web-search, cite
- [ ] 2. Load the candidate's XI + bench, each player's nation, fixture, kickoff slot, and xEV (read player-ev signals; do NOT re-derive)
- [ ] 3. KICKOFF SPREAD — bin the XI (and squad) by day/slot; score the spread; raise over-stack flags
- [ ] 4. BENCH ORDER — rank the 4 bench by kickoff time (latest = highest), break ties by xEV; drop dead-fixture benchers to the floor
- [ ] 5. SUB TRIGGERS — for each early starter, generate a conditional promotion rule; set the threshold T by position and the bench player's own xEV
- [ ] 6. Cross-check against the captain ladder (shared kickoff sequence) — flag conflicts, don't re-solve the ladder
- [ ] 7. Emit the matchday-timing signal: kickoff_spread + over_stack_flags, bench_order[1–4], sub_triggers[]