fix(sync): skip archived repos and guard doc collisions

[hanthor]

Summary

• exclude archived repositories from the org-wide documentation sync
• keep the listing completeness check aligned with the active-repo filter
• add a CI guard for case-insensitive duplicate paths under docs/
• cover the collision detector with unit tests

Why

Archived repos can reintroduce stale hanthor/ references into generated pages. Case-only filename differences such as USER-GUIDE.md and user-guide.md break checkouts on case-insensitive filesystems and can produce duplicate routes.

Validation

• node --check scripts/sync-org-docs.mjs
• node --check scripts/check-doc-collisions.mjs
• node scripts/__tests__/sync-org-docs.test.mjs (71 passed)
• node scripts/check-doc-collisions.mjs
• git diff --check

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