[#5175] rollmode sources foundation

[Kapuzenjoe]

Maybe Closes #5175

Builds the data foundation for surfacing advantage/disadvantage source labels on the sheet and in roll dialogs.

Changes:

• Extends modeCounts on AdvantageModeField with sources[] and overrideSource (captured automatically during Active Effect application via change.effect, or explicitly via setMode({ source }))
• Adds { label: true } option to hasConditionEffect to return the responsible condition label directly instead of a boolean
• Adds AdvantageModeField.collectSources(model, keyPaths) (parallel to combineFields, returns a flat list of { value, source } entries for attribution)
• Adds Actor5e#_prepareRollModeAttributions(keyPaths): resolves collected sources to AttributionDescription[], handling pre-resolved labels, lazy Active Effect resolution, and manual toggles
• Updates all setMode call sites (armor, conditions, flags) to pass a source

Usage (e.g. #7081):

// Get resolved attribution entries for a roll's advantage sources:
const attributions = this._prepareRollModeAttributions([
  "abilities.dex.check.roll.mode",
  "skills.acr.roll.mode"
]);
// → [{ value: 1, label: "Poisoned", document: null }, ...]

[thatlonelybugbear]

Nice. I can rework #7081 based on this if it goes ahead.

[revilowaldow]

Very keen to see this system implemented <3 thank you everyone who's contributed so far