enhancement(ui): flat DAW redesign — mixer, topbar, waveform, and sidebar polish #44

Summary

Full UI overhaul to a flat dark DAW aesthetic for the alpha release. Several iterative polish fixes were required after the initial redesign.

Changes included

Mixer

• Horizontal fader layout (icon → name+VU → fader → dB value → M/S/DL)
• VU meter displayed below stem name
• Volume fader expanded, dB labels (0.0 dB at unity, ±dB values on drag)
• Stem icons removed from mixer rows
• Stem row height increased

Topbar

• Link and lightning icons removed
• Height increased for readability

Waveform / ruler alignment

• .daw-mixer-label and .daw-wave-label widths matched to .daw-stems-panel to fix playhead and ruler misalignment

Sidebar

• Trash bin rail button restored
• "Empty trash" button added to trash view (red-tinted, shows only when in trash view)
• Folder header hidden when in trash view

Release

0.5.0-alpha.1