Dashboard charts do not render; move dashboard JS to a library file

Problem/Motivation

The three dashboard charts stay blank after installation. Chart.js is loaded through
the Drupal library system, which places it in the page footer, but the chart-building
code runs from an inline <script> tag earlier in the page.
The browser reaches the inline script before Chart.js is available and throws
ReferenceError: Chart is not defined, so no chart is drawn.
The chart data is also printed directly into that inline script with
json_encode|raw, which trips the project's ESLint job.

Steps to reproduce

1. Install ai_metering, configure a provider, and sync pricing.
2. Make a few AI calls so usage rows exist.
3. Open /admin/reports/ai-metering.
4. The three charts (token split, cost by provider, cost by model) are blank. The browser console shows ReferenceError: Chart is not defined.

Environment

• Drupal version: 11.3.11
• ai_metering version: 1.0.0-alpha1
• AI provider module + version: any (e.g. ai_provider_anthropic 1.x)
• AI feature module tested: N/A

Proposed resolution

Move chart rendering, table sorting, and the month filter into a dedicated JavaScript
file (js/ai-metering-dashboard.js) attached through the
ai_metering_dashboard library with core/drupalSettings,
core/once, and the Chart.js library as dependencies.
Pass chart data through drupalSettings instead of a raw inline script.
This fixes the load order, eliminates the inline script, and clears the ESLint findings.

Remaining tasks

• Move the inline script to js/ai-metering-dashboard.js as a Drupal behavior.
• Pass chart data via drupalSettings from the controller.
• Declare library dependencies (drupalSettings, once, chartjs).
• Verify the charts render with no console errors.
• Review.

User interface changes

Yes — the three dashboard charts now render correctly.

API changes

N/A

Data model changes

N/A

AI assistance

N/A