docs: remove ROS references and meta sections from documentation

[thetooler]

Summary

The library never depended on ROS, but its docs and comments described it as the
"ROS-agnostic" layer of a ROS stack, which read as ROS-adjacent to anyone
opening the repository cold. This removes every ROS reference, and drops the
project-management sections from the readmes: the version-scope notice, the
license restatement, and the red-lines note.

No behavior change — comments, descriptions, documentation and the pkg-config
Description field only.

Changes

• ROS wording removed from README.md, README_zh.md, CMakeLists.txt, package.xml, cmake/litegrip_cpp.pc.in, examples/CMakeLists.txt, src/version.cpp, src/control_loop.cpp, src/safety.cpp, and the control_loop.hpp / gripper.hpp / safety.hpp / can/controller.hpp headers.
• Where the prose carried information, it was rewritten rather than cut: "ROS-side gate" becomes "the old Python gate", "the node" becomes "the process", ## Non-ROS usage becomes ## Minimal example, my_node becomes my_app, "layer 1" becomes "the bottom layer".
• package.xml is kept, since it declares the plain-cmake package. Its description is rewritten and the download.ros.org schema processing instruction is removed; the file stays well-formed XML.
• The colcon / ROS-workspace build note is gone from both readmes and from the CMakeLists.txt design constraints.
• ## What is not in this version / ## 本版本不包含, ## 许可证, and ## Red lines are not yet unit-specific / ## 红线尚未按本台夹爪重建 are deleted — 35 lines, all deletions, nothing added.
• The deleted red-lines warning is not lost: it ships with the library in calibration/safety_limits_350.json (★ NOT VERIFIED ON THIS UNIT, plus the re-derivation and max_feedback_velocity_rad_s note) and in include/litegrip/safety.hpp. The v1 capability scope stays in the include/litegrip/gripper.hpp header comment.

Testing

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release   # clean rebuild, no warnings
cmake --build build -j
ctest --test-dir build --output-on-failure       # 100% tests passed, 0 tests failed out of 12
npx --yes markdownlint-cli2@0.23.3 "README.md"   # 0 issues (the CI check)
python3 -c "import xml.dom.minidom as m; m.parse('package.xml')"   # well-formed

No hardware and no CAN interface required — this is the same suite CI runs.

Issues

None — no issue tracks this change.