chore(github): add issue forms and reporting guidelines

[KraHsu]

Summary

Adds a full issue-intake setup — GitHub issue forms plus written rules — for a repo that previously had neither.

Issue forms (.github/ISSUE_TEMPLATE/):

• Bug report — pre-flight checklist (searched duplicates, checked README Troubleshooting, not a pure-Genesis bug), required repro steps, a required environment block with a copy-paste version one-liner (genelab / genesis / torch / CUDA), and RL-backend + sim-backend (SimulationCfg.gpu) dropdowns. Auto-labels bug.
• Feature request — area dropdown matching the module layout (CLI, registry/configs, managers, asset zoo, RL backends, scene/terrains/sensors), motivation + proposal required. Auto-labels enhancement.
• Documentation — page URL/path plus a language-variant dropdown reflecting the mandatory .en.md / .zh.md parity. Auto-labels documentation.
• Question / help — docs-first checklist. Auto-labels question.
• config.yml — blank issues disabled; contact links route to the docs site and to the Genesis upstream tracker for simulator bugs.

Rules — new ## Reporting issues section in CONTRIBUTING.md: search first, one problem per issue, README-Troubleshooting pitfalls are not bugs, upstream routing for pure-Genesis reproductions, reproducibility requirements, and label/triage expectations. Issues welcome in English or 中文.

Test plan

• All five YAML files parse cleanly (yaml.safe_load)
• After merge: github.com/KraHsu/GeneLab/issues/new/choose shows the four forms + two contact links, and blank issues are blocked

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