Make ancestry walk limit configurable via CmsServiceOptions #5

Context

_validateAncestry in CmsService uses a hardcoded walkLimit = 200. For long-lived articles with 200+ versions, valid older SHAs get misclassified as history_walk_limit_exceeded.

Proposal

Extract the walk limit into a CmsServiceOptions field (e.g., ancestryWalkLimit) with a sensible default (200). This lets callers tune it per-deployment without code changes.

References

• src/lib/CmsService.js L327
• PR feat: version history browser (CE3) #4 review discussion (CodeRabbit R1, comment on hardcoded walkLimit)