feat(asset.graph): add config panel and fix grid cell alignment

[Paulopk0]

📝 Description

This PR unifies the visual identity of the chart settings panel with the styling patterns used in the rest of the Plata ecosystem (adopting a 100% flat design, removing all shadows, integrating the #6a4c93 brand purple, and using the Montserrat font). Additionally, it localizes the entire interface and code comments to English and implements real-time preview synchronization between the settings panel and the chart page.

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🛠️ Changes

1. Styling & Visual Identity (Plata Brand Theme)

• Plata Color Palette Alignment:
  • Modal/Content Background: #ffffff (White).
  • Sidebar & Footer Background: #f2f2f2 (Light gray, matching main admin layout rails).
  • Accent/Active Highlights & OK Button: #6a4c93 (Plata Purple) with hover states at #5a3d82.
  • Typography Colors: #000000 (Pure Black) and #666666 (Dark Gray).
• Montserrat Typography: Enforced the Montserrat font family as the default across all settings panel writings (titles, select dropdowns, labels, ranges, and buttons) using general inheritance rules.
• Geometry and Alignment (8px Grid):
  • Unified all element spacing/gaps to a symmetric 8px grid.
  • Standardized the select element height to 28px to perfectly align with color picker containers.

2. Real-Time Settings Synchronization

• Implemented the Web BroadcastChannel API (using channel name chart_settings_sync) inside both index.php and asset.graph.config.php.
• Modifying theme presets, font family, sizes, or line thickness inside the settings panel now immediately reflects in any open chart window in real time without reloading.
• Previews are saved locally in the browser (localStorage) and committed permanently to the server's asset.graph.config.json once the user submits the form.