Choose how the grippers SDK is delivered to ROS consumers (submodule vs vendor package)

[ebarnett3]

Deferred from the review of #20 — a strategy decision, not a code change.

Problem

The repo vendors the SDK as a git submodule at extern/grippers. It builds, and colcon picks it up, but it forces every consumer to clone recursively: a plain git clone followed by colcon build fails with a confusing missing-CMakeLists error. That is a poor first experience.

Options on the table

• git submodule (status quo) — no infrastructure, requires --recurse-submodules.
• Vendor/wrapper ament package — a small vendor package that fetches and builds the SDK at build time, the way libserialport-style vendor packages do. The reviewer's preference: least effort of the alternatives, and no recursive clone.
• Further options are laid out in the PDF attached to the discussion: ROS C++ SDK Integration Strategies.pdf

Considerations

• The SDK is versioned independently of this repo, so whatever we pick has to pin a version and make bumping it reviewable.
• Offline and air-gapped builds: a vendor package that downloads at build time breaks them, a submodule does not.
• Once the SDK is released and installable, a plain find_package against a rosdep-installed SDK becomes the endgame — this choice should not block that.

Discussion

#20 (comment)