feat: add admin configuration for per-season scoring rules

[adrunkhuman]

Goal

Expose per-season scoring-rule configuration in the admin surface once scoring rules are persisted.

Depends on

• feat: add per-season configurable scoring rules #50 per-season scoring rules
• centralized scoring/recalculation service
• season model

Scope

• show the active season's scoring rules to admins
• allow admins to update the active season's basic scoring values
• handle already-scored fixtures safely: block changes, require confirmation, or trigger explicit recalculation
• update user-facing scoring/help text to reflect configured rules

Initial rule fields

• exact score points
• correct outcome points
• wrong outcome points
• late full prediction penalty behavior

Non-goals

• no formulas/plugins
• no double-points fixture setup
• no streak bonuses
• no cross-server shared presets

Acceptance criteria

• admins can view and change scoring rules without code or env changes
• changed rules affect future scoring for that season
• already-scored fixtures cannot silently remain stale after rule changes
• user-facing scoring text is dynamic or avoids hardcoded claims
• tests cover changed rules and the stale-score safety path