Real bracketed multi-main: per-tier config + builder UI (follow-up to seeding composition)

[ryan-johnson2]

Follow-up to the real (bracketed) MultiGP multi-main, now composable from atomic rounds. Distinct from the older flat-mains plan in #219/#234: each main is its own single-elim bracket (heats of N), wired bottom-up by the new range/union seeding rules, with per-tier finals.

Shipped (the foundation)

• feat(seeding): range + combine seeding rules (foundation for real multi-main) #323 — new seeding rules: FromRankingRange { source_rounds, skip, take } (ranking slice) + Combine { sources } (union, concat + dedupe-keep-first); recursive resolve_seeding with a depth guard (also closed a latent seeding-cycle stack-overflow).
• feat(tournament): compose+run the real MultiGP multi-main (64-pilot) + fix 4-up FromHeatWinners #324 — proved the full composition end-to-end (contract test) + fixed a real 4-up bug (FromHeatWinners kept the wrong advancers on 4-up levels via Generator::advancers()). Live-verified at 64 pilots on the rig: qual → C/B/A mains (brackets of 4-pilot heats) → bumps land → A-main Chase-the-Ace final → champion; every heat exactly 4 pilots.

The structure is currently composed via the API/script (run-real-multi-main.mjs), NOT authorable in the console.

Future work

• Configurable tier count — A, B, C, … N (currently the 3-main shape is hardcoded in the script). The builder should take a tier count + per-tier entry/bump counts.
• Per-tier win condition — each main its own win condition (e.g. C/B First-to-N, A Most-laps, or different lap targets), instead of one shared condition. (Per-tier final format — single race vs Chase-the-Ace — is already expressible per round; surface it per tier in the builder.)
• Builder UI / wizard (S3) — a single "Real Multi-Main" action that emits the whole round set in dependency order: a realMultiMainReqs(...) planner in frontend/apps/rd-console/src/lib/standings.ts + a wizard that previews the qual-rank partition (seeds 1-6 / 7-12 / 13-20) and the bump arrows, then POSTs the rounds. Needs a FromRankingRange/Combine authoring affordance in the seeding picker.
• Bump-ladder viz — show the tier→tier bump arrows in the standings/bracket view.

Relates to #219 (first-class multi-main), #234 (bump-ups). The seeding primitives + composition are done; this issue tracks per-tier configurability + making it authorable without scripting.