[Epic] Implement Neo.container.Fragment

Implement a Neo.container.Fragment that allows grouping items without rendering a wrapper DOM element.

Core Requirements:

1. No Wrapper Node: Renders as a range of sibling nodes in the DOM (anchored by Comments), allowing children to sit directly in the parent's layout context (e.g., CSS Grid).
2. Container Capability: Supports items config to manage child components.
3. VDOM Structure: Uses tag: 'fragment' in the VNode tree to maintain Component-to-VNode symmetry.
4. Smart Runtime Architecture: The VDOM Helper generates high-level Fragment Deltas, and the Main Thread (DeltaUpdates) handles the complex DOM range manipulation locally to minimize IPC.
5. Multi-Window Support: Seamlessly moving a Fragment container (and its children) to a different browser window must work out-of-the-box.
6. Non-Destructive Moves: Moving items into, out of, or within Fragments in the same window must NOT trigger re-rendering (no destroy/create). It must use physical DOM moves.

Acceptance Criteria:

• Fragment renders with Comment Anchors (<!-- fragment-id-start -->) and no wrapper element.
• Fragment children participate correctly in parent CSS Grid/Flex layouts.
• Moving a Fragment to a new window works correctly.
• Moving items in/out of Fragments preserves their DOM state (focus, input values).