Edicts Slice 1: Net-Modifier Engine (enabler)

[Quantumheart]

Part of #510.

Foundation for negative civilization modifiers. No edicts yet — net behavior matches today, but sub-1.0 multipliers become possible.

Scope

• New CivilizationNegatives record (mirror of CivilizationBonuses + new cost types).
• New CivilizationModifierResolver — combines milestone bonuses (positive) + signed edict effects → net per lever, clamped.
• Rewrite the four > 1.0f apply-site guards to apply the resolver's net multiplier unconditionally: FavorSystem.cs:383 (favor), FavorSystem.cs:424 (prestige), PvPManager.cs:202 and 225 (conquest).
• Stacking math + clamps: Favor/Prestige floor 0.5 cap 3.0; Conquest floor 0.0 cap 3.0; holy-site cap floor 1; death-favor-loss cap 1.0.

Acceptance

• Resolver returns net == current values when fed only milestone bonuses (regression).
• A negative test delta produces a sub-1.0 multiplier that actually applies at the grant site.
• Unit tests for resolver math + clamps.

Blocks: all other slices.