1700b4a1e543fffc7c8c5c56f137203d6799eee7  [GFC] Resolve auto-fill repetitions against the grid container's min and max size when computing intrinsic widths

Classified as not security-relevant.
Triage note: Introduces AutoRepeatConstraint and threads preferred/min/max sizes through ExplicitGridResolver/GridFormattingContext so auto-repeat resolves against container min/max. CSS grid layout feature/refactor; no security relevance.
This commit was flagged by the signal scorer and reviewed by AI (not a human). It is listed only so the triage is auditable; there is no root-cause analysis because this is not a vulnerability fix.

Structural signals: smartptr_member_added (+4.87), null_guard (+1.95), clamp_saturate (+1.8), area:Source/WebCore/layout (+2.0)