v3.5.0

Added

• Vector magnitude (VM) overlay: orientation-independent fourth signal trace, toggle via the plot legend
• Walking detection (Urbanek 2015 sustained harmonic walking): FFT-based detector on VM with hysteresis thresholds, gap-bridging, and 10s sustained-duration filter
• Walking-suggestions sidebar panel: scrollable click-to-jump candidate list with per-row dismiss/reinstate toggle, persisted in a shared walking_suggestions.xlsx and auto-loaded on session start
• 15 reference images from the NSHAP annotation guidelines and Urbanek 2015 Figure 2 in docs/images/

Changed

• Rewrote docs/annotation-guide.md based on the NSHAP annotation guidelines
• Added Vector magnitude and Walking detection sections to docs/usage.md
• Tightened prose across README and docs