[Stage 1.2] Move @gravity-ui/graph into packages/graph

[draedful]

Parent: #318

Goal

Move the current public library into its final workspace location without splitting functionality or introducing additional public packages.

After this task, the repository root orchestrates the workspace and packages/graph owns the complete @gravity-ui/graph artifact.

Scope

• Make the repository root a private workspace project.
• Move the public package manifest, sources, tests, and package-specific build configuration into packages/graph.
• Preserve the current root and React public entry points for this migration step.
• Update root scripts, TypeScript configuration, test configuration, and tooling paths for the new location.
• Keep package-local files and published assets owned by packages/graph.
• Run the tarball consumer checks introduced in Stage 1.1 against packages/graph.

Acceptance criteria

• packages/graph is the only workspace project named @gravity-ui/graph.
• The repository root is private and cannot be published accidentally.
• @gravity-ui/graph builds and packs independently from packages/graph.
• Vanilla JavaScript and React tarball consumers pass without source aliases.
• Unit tests, Storybook build, and E2E checks pass from a clean checkout.
• No functionality is intentionally extracted into another public package in this task.