refactor!: reduce InfiniCore to a component manifest

[voltjia]

Summary

• Reduce InfiniCore to a component manifest containing only its license, manifest documentation, contribution guidelines, and the InfiniRT, InfiniOps, and InfiniCCL gitlinks.
• Pin InfiniRT at 08677bb566ee3009586ae4194e6f7e50a4bbad66, InfiniOps at 296271487beb594a248fd463e5fff14f7ab74293, and InfiniCCL at 1f3e24a68448c3f2af4475d603ed7c2b85e28f12.
• Remove the legacy runtime, operator, Python package, build system, tests, scripts, and repository workflows from this repository.
• Add a focused CONTRIBUTING.md that consolidates the shared commit, branch, pull request, and validation conventions used by the component repositories.

Motivation

InfiniCore should coordinate compatible component revisions instead of maintaining duplicate runtime and operator implementations. Keeping a single authoritative implementation in each component removes the legacy API surface and makes the repository boundary explicit.

Repository Surface

The resulting repository has exactly seven tracked paths and no build or packaging entry point of its own. README.md documents the manifest role, recursive submodule checkout, and contribution guide.

Breaking Change

InfiniCore no longer provides the legacy in-tree runtime, operator, build, packaging, or Python APIs. Component implementations are provided exclusively by the pinned submodules.

Validation

• Verified git ls-files returns exactly the seven intended paths.
• Verified all three component entries use gitlink mode 160000 and resolve to the pinned revisions.
• Verified git submodule update --init --recursive --depth 1 checks out the complete component graph.
• Verified neither the final tree nor the PR commit range contains the removed legacy status type.
• Verified the branch name, commit messages, and pull request title follow the Conventional Commits conventions documented in CONTRIBUTING.md.
• Verified git diff --check origin/issue/1373...HEAD passes.

Supersedes #1405, which GitHub closed automatically when its head branch was renamed.

Closes #1373