Upgrade GUI with premium metallic styling and 3D waveform visuals

[BustaBitBotScript]

Motivation

• Refresh the UI to feel like high-end mastering hardware with stronger tactile cues, metallic surfaces and layered lighting.
• Improve the waveform visualization to present a more powerful, analyzer-style 3D look for better visual feedback during mastering.

Description

• Introduced new theme variables and layered background textures (body::before/body::after) to create a darker studio backdrop and subtle sheen (changes in web/styles.css).
• Restyled control surfaces (transport buttons, toggles, sliders, cards, presets) with metallic gradients, bevel-style shadows, adjusted sizes, and hover/press depth to make switches feel sculpted and premium (changes in web/styles.css).
• Upgraded waveform panel visuals and container styling (larger height, rounded corners, panel gradients, borders, inset shadows) and increased waveform rendering fidelity by switching WaveSurfer to taller, bar-based rendering with richer gradients and updated cursor styling (changes in web/styles.css and web/ui/waveform.js).
• Kept existing interaction and memory-cleanup behavior for WaveSurfer (blob URL management, hover handler and seek callbacks) while changing rendering parameters (height, barWidth, barGap, barRadius) and gradient stops (changes in web/ui/waveform.js).

Testing

• Ran npx vite build (client + electron preload/main bundles) and the build succeeded.
• Ran npm run build where Vite/electron compile steps completed but packaging failed due to a blocked Electron binary download in this environment (electron packaging failed with a GitHub download error).
• No unit tests were modified; visual changes were validated by building the frontend bundle locally.

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Codex Task