Rulesets are live references; editing one silently restates completed seasons

[alchemydc]

Deferred from the PR #99 review. This is a product decision, not a bug — filing it so the current behavior is chosen rather than inherited.

The inconsistency

Two halves of one concern ended up with opposite immutability policies:

• Season.rulesetId is a live reference. Editing a ScoringSystem immediately restates standings for every season pointing at it. A dropCount edit silently rewrites prior championship results.
• PAX factors went the opposite way and were frozen per entry (Entry.paxIndexApplied, read via appliedPaxIndex()), specifically so history can't be rewritten by accident. A PAX-table edit only affects existing entries after an explicit per-season re-apply.

Defaults amplify it

Both createSeason (apps/web/src/lib/create-season.ts) and resolveOrCreateSeason (apps/web/src/lib/season-resolve.ts) attach the league's oldest ScoringSystem row when none is named. So sharing one ruleset across every season is the default state, and a single edit reaches all of them.

The preset.update audit does snapshot before/after, which is good and clearly deliberate — but there is no freeze on completed seasons and no copy-on-write.

Proposal

For a club championship archive: refuse a ruleset edit that would alter a season whose status is completed, and provide an explicit clone-and-re-point path (duplicate the ruleset, assign the copy to the active season, edit the copy).

Alternative worth considering: snapshot the policy onto the Season at completion, mirroring what Entry.paxIndexApplied already does for PAX.