Implement sensor reading filter/debounce (waves, debris)

[xishell]

Description

Add filtering logic to reject false occupancy triggers caused by waves, debris, birds, or other transient objects. The filter should require sustained presence across multiple consecutive wake cycles before changing the reported state.

Acceptance Criteria

• A single anomalous reading does not change the reported state
• State change requires sustained detection across a configurable number of consecutive cycles
• False positive rate is significantly reduced compared to raw threshold detection

[xishell]

Already implemented in components/dp_radar/dp_radar_filter.c: proximity threshold (CONFIG_DOCKPULSE_PROXIMITY_CM, default 30 cm) plus stability window of N consecutive frames (CONFIG_DOCKPULSE_STABILITY_FRAMES, default 2 → ~400 ms debounce). HMMD's near-field distance estimator is reliable enough that gate-energy thresholding/background subtraction aren't needed — see Kconfig comment in main/Kconfig.projbuild:73-75.