Feat/equalizer

[Deep-Jiwan]

Add 8-Band Parametric Equalizer

• Bottom Bar Equalizer Widget: Compact equalizer interface added into the player's bottom bar with icon, preset selector, and ON/OFF toggle
• 8-Band Parametric EQ: 8 frequency bands (60Hz, 150Hz, 400Hz, 1kHz, 2.4kHz, 6kHz, 12kHz, 15kHz) supporting gain range from -12dB to +12dB
• Preset System: Pre-configured presets. Not implemented saving custom presets/creating new/ import/export, but custom set presets remains in localStorage across browser refreshes. Or so i believe

Implementation Details:

• Web Audio API: Uses BiquadFilterNode to create a 10-node filter chain for smooth, high-quality audio processing
• Persistence: localStorage integration for automatic save/restore of custom presets and settings

UI/UX Features:

• Smooth Animations: 1-second ease-out transitions when switching presets
• Real-time Feedback: Visual gain value display and gradient slider fills
• Preset Cycling: Scroll on icon to quickly cycle through presets
• Pin Feature: Pin equalizer popup to keep it visible while interacting with UI
• Wheel Control: Scroll on sliders to fine-tune individual bands
• Quick Toggle: Single-click on icon to enable/disable EQ
• Custom Preset: Auto-saves manual adjustments as "Custom" preset

Files Changed and Components:

• Added src/assets/icons/equalizer.svg -> SVG icon
• Added src/components/BottomBar/Equalizer.vue -> Main component and UI for adjusting the EQ
• Added src/stores/equalizer.ts -> storage and manage EQ state
• Modified src/components/BottomBar/Right.vue -> Added EQ to player bar
• Modified src/stores/player.ts -> Connect EQ to audio pipeline
• Added src/utils/equalizer/eqPresets.ts -> manage pre-configured presets
• Added src/utils/equalizer/equalizer.ts -> Web Audio API wrapper with 8-band BiquadFilterNode filter chain, audio routing, gain smoothing, and resource cleanup
• Added src/utils/equalizer/presets.json -> The pre-bundled presets

Note to Reviewer:

• I am not a very veteran developer. Just a guy with a vision. I needed this feature and used my best knowledge and help from Sonnet 4.5 to best implement this in a simple way. I thought it might be useful to others and so i am presenting this. If the code is heavily unusable (not safe or a lot of AI) then i understand that this pull request may not be merged.
• If there are any changes then i am happy to do them. and then if the code is well and good then im glad i was able to help make this application better as i daily run this app myself.

[CLAassistant]

All committers have signed the CLA.

[Deep-Jiwan]