[Roadmap] Documentation hub for HugeGraph Rust modernization

## Goal

Provide the documentation and contributor entry point for HugeGraph's **incremental Rust modernization** across Toolchain, Server/HStore/PD, and graph computing.

This issue tracks documentation work; it does not imply rewriting the documentation website itself in Rust. The project is an incremental experiment, not a commitment to replace every existing implementation.

## Roadmap at a glance

```text
Toolchain ─────┐
Server/PD ─────┼─> Documentation hub
Computer ──────┘ │
├─ architecture and status
RFC -> PoC -> tests ──┼─ compatibility and migration
-> preview ├─ benchmarks and tutorials
-> adoption └─ contributor guide

Documentation is updated at every delivery gate, not after the rewrite.
```

## Documentation scope

1. **Architecture and status**
- A project-wide roadmap and per-repository status.
- Clear ownership, maturity (`experiment`, `preview`, `production-ready`), non-goals, and known limitations.
2. **Contributor guide**
- Rust toolchain setup, workspace conventions, style/lint/test commands, dependency policy, and how to propose a child project.
3. **Compatibility and migration**
- API/CLI, protocol, storage/data-format, and platform matrices.
- Coexistence, upgrade, downgrade, and rollback instructions.
4. **Evidence**
- Reproducible benchmark methodology and results.
- Tutorials and troubleshooting for opt-in Rust components.

Documentation should describe only implemented or explicitly proposed behavior; it must distinguish plans from released features.

## Candidate work items

- [ ] Add an overview page linking all repository parent issues
- [ ] Define shared terminology and maturity labels
- [ ] Add the Rust contributor environment/style guide
- [ ] Create compatibility and supported-platform templates
- [ ] Create a reproducible benchmark-report template
- [ ] Document the first accepted proof of concept
- [ ] Add migration, rollback, and troubleshooting guides before any preview release
- [ ] Keep English and Chinese navigation/content aligned

This checklist will link to concrete child issues as proposals are accepted.

## Project-wide roadmap

- Toolchain: apache/hugegraph-toolchain#748
- Server / HStore / PD: apache/hugegraph#3110
- Computer / Vermeer: apache/hugegraph-computer#355
- Documentation hub (this issue): apache/hugegraph-doc#462

## How to participate

Interested in **open source, Rust, technical writing, internationalization, developer experience, or infrastructure**? Comment with the area you want to help with. Documentation, diagrams, tutorials, benchmark reproduction, and translation are excellent entry points.

First-time contributors can start with the [HugeGraph contribution guide](https://hugegraph.apache.org/docs/contribution-guidelines/contribute/) and the repository's `good first issue` / `help wanted` tasks.

Start with the HugeGraph contribution guide and the linked Toolchain, Server/HStore/PD, and Computer child issues to identify an accepted documentation proposal. Use the checklist to define a focused child issue; done means the selected roadmap, contributor, compatibility, evidence, or migration content is implemented and its plan-versus-release status is clear.

Written by the indexing model from the issue text.