v0.3.4

Added

• Spectrum: M/S + L/R channel overlay with dual-curve display
• Spectrum: peak-hold filled-area rendering (replaces dashed line)
• Spectrum: peak-hold toggle chip in panel header
• Spectrum: combined / L/R / M/S view toggle in panel header
• Spectrum: color-coded hover dB rows in overlay mode
• Spectrum: secondary curve legend and 2-row hover tooltip

Fixed

• Timeline: stabilize initial history viewport
• Workspace: show panel header chip in fullscreen overlay
• CI: resolve clippy errors on Windows