* feat(repo): expose ResolveVersion + ReadFileAt for symbolic versions

Repo.ReadFile took a raw int64 RID, leaving every library caller to re-implement symbolic-version resolution (tip, trunk, branch name, UUID prefix) — work the CLI's resolveRID already does inside the cli package. Move the resolver onto Repo as ResolveVersion, refactor cli/shared.go to call it, and add Repo.ReadFileAt(version, path) so callers can read by name without first calling ResolveVersion themselves.

Adds ErrVersionNotFound for the not-found case and an ambiguity error for prefix collisions.

* chore(cli): drop unused openInternalRepo helper + repo import

Now-dead code: resolveRID was its only caller, and resolveRID is now a one-line wrapper around Repo.ResolveVersion that doesn't need the inner handle. Also removes the now-unused internal/repo import that the helper brought in, and refreshes the cli SDK page accordingly.

* chore(go.work.sum): pin transitive deps from docs toolchain

gomarkdoc pulls these via go install during make docs-gen-sdk; commit the lockfile entries so contributors see no go.work.sum drift after a docs build. check-in: 7eb46a9635 user: [email protected] tags: trunk