feat(tools): S7 SLAM-features inspector — real EuRoC → persistent landmark state

[Ravenwater]

Per-stage inspector for epic #371. Depends on #372, #373. Renderer: 3D tier (after S5).

• Input: tracks + state (trace).
• Transformation: SLAM-feature initialization/maintenance in the state.
• Output: persistent landmarks in state + covariance.
• Viz (3D tier): persistent vs MSCKF landmarks, anchor changes over time.
• Decouple behind an S7 I/O struct.