docs: streamline roadmap and PR governance

[TATP-233]

Summary

• 以独立交付价值和完整纵向切片定义 issue 粒度，移除文件数和 LOC 的机械拆分线
• 为 roadmap 定义 declared base、集成分支、child PR 和嵌套 roadmap 流程
• 每个 PR 以本地 make test-all 为 gate，仅实际 base 为 main 的 PR 运行远程 CI
• 同步 AGENTS、双语贡献文档、架构验证说明及 GitHub issue/PR 模板

Linked Work

• Issue: none; repository governance update requested directly
• Parent roadmap: none
• Roadmap declared base: none
• Milestone: none
• Base branch: main

Validation

• make test-all passed on the final local head before this PR was created
• Additional documentation and template validation completed

Commands actually run:

UV_PROJECT_ENVIRONMENT=/tmp/unilab-governance-gate.kyxxJc/.venv uv sync --python 3.13 --extra mujoco --extra motrix
UV_PROJECT_ENVIRONMENT=/tmp/unilab-governance-gate.kyxxJc/.venv make test-all
uv run pytest tests/scripts/test_check_docs.py tests/scripts/test_repo_hygiene.py -q
UNILAB_DOCS_SKIP_AUTODOC=1 uv run --no-project --with-requirements docs/sphinx/requirements.txt sphinx-build -b html -n docs/sphinx/source docs/sphinx/build/html
uv run --with check-jsonschema check-jsonschema --schemafile https://json.schemastore.org/github-issue-forms.json .github/ISSUE_TEMPLATE/work_item.yml
git diff --check

Results:

• make test-all: 1776 passed, 24 skipped, 1 xfailed; benchmark module/script smoke passed
• focused documentation and hygiene tests: 26 passed
• Sphinx build: passed
• GitHub Issue Form schema: passed
• diff whitespace check: passed

The clean gate used the MuJoCo+Motrix dependency profile. An initial run in the existing mjwarp-enabled developer environment exposed a pre-existing benchmark import-order side effect; both affected tests pass in isolation, and no unrelated source fix is included here.

Remote CI route:

• Head: 287ff55364573932d207ea9abf0b0a3171ea4dd4
• CI run: all 6 jobs passed
• Docs run: passed

Impact

• Backend impact: none
• Platform impact: none
• Training effect expected: no

Checklist

• Updated docs for the workflow change
• Kept English and Chinese developer guidance synchronized
• Updated issue and PR templates
• Noted validation and follow-up context explicitly