GPS Reader

TODO:

• [ ] Add page-specific notes for autonomy-stack/navigation/gps-reader.md after inspecting the real project files.
• [ ] Cross-link GPS Reader to the most relevant code, data, testing, and safety pages.
• [ ] Document the exact input entering this subsystem.
• [ ] Document the exact output leaving this subsystem.
• [ ] Map the subsystem to the owning runtime file or module.
• [ ] Describe the control priority when this subsystem disagrees with another subsystem.
• [ ] List the settings, constants, and flags that change this behavior.
• [ ] Add a failure-mode checklist for field testing.
• [ ] Add how to verify the subsystem on the bench before a driving test.
• [ ] Add how to verify the subsystem during a real outdoor run.
• [ ] Document graph input, start/goal selection, route output, and segment output.
• [ ] Add a route example showing AI/manual split and handoff behavior.
• [ ] Document GPS message type, fix quality, satellites, and coordinate units.
• [ ] Add how poor GPS affects route selection and dashboard status.
• [ ] Add the exact source path, artifact path, or hardware component name.