docs(core): fix published frame adapter reference links

[jrusso1020]

The core schema reference links to two documents that no longer exist. Point readers to the current frame adapter and determinism concept pages using public URLs, which also work from the published core package.

Successor to #1942 by @tianma-if; original authorship preserved. The proposed repository-relative replacements would escape the installed package.

Validation: both public pages resolve; package contents and adjacent local links checked; whitespace and all applicable commit hooks pass. The repository formatter skips this file.

[miguel-heygen]

Reviewed 29781e19d5b8d1ebfbd6ce021a121de5b3a94826. No findings.

packages/core/docs/core.md:7 now links to the public frame adapters and determinism pages. Both resolve to the intended documentation. The package publishes docs, so absolute URLs also avoid escaping an installed package directory.

Validation: full one-line diff, package file inclusion, and both live destinations checked. No prior reviews or comments; CI had no observed failures, with jobs still running. This is a documentation review; no runtime behavior claims.

Verdict: APPROVE
Reasoning: Both replacements are relevant, reachable, and valid outside a repository checkout. Pending CI must complete before merge.

— Magi