PixEagle v7.0.0-beta.28

Ubuntu and Raspberry Pi acceptance candidate.\n\nHighlights:\n- Reuses verified Python, AI, dlib, OpenCV/GStreamer, and dashboard components during repair/update.\n- Makes config and dashboard-environment reset one validated backup/rollback transaction.\n- Corrects Classic estimator initialization and elapsed-time prediction while keeping prediction-only output follower-ineligible.\n- Adds default-on, schema-backed follower engagement confirmation.\n- Renames the Classic segmentor action to Selection Assist and documents SmartTracker detect/OBB support; Smart segment models remain deferred.\n- Preserves dashboard/API availability when optional video, MAVLink2REST, or MAVSDK providers are unavailable.\n\nBeta.28 supersedes beta.27, whose runtime and tests passed but whose CI found one test-only lint-contract violation. No runtime behavior changed in the correction. Ubuntu update/reset, Raspberry Pi, physical camera/gimbal, PX4, QGC, and field acceptance remain separate gates.