fix(web): metrics dashboard SoC chart text freezes on first-load value

[chalfontchubby]

Summary

Fixes #4151. The battery SoC doughnut chart's center text (percentage and kWh figures) is drawn by a Chart.js afterDraw plugin registered once in mdInitSOCChart. That plugin closed over the pct/d values from the moment the chart was first created. On each 30s refresh, mdUpdateSOCChart only mutates the existing chart's data array and calls .update() - it never recreates the chart (mdRenderAll only calls mdInitSOCChart again if mdSocChart doesn't exist yet) - so the doughnut ring's fill proportion updated correctly but the on-screen number text stayed frozen at the first-load reading, while every other card on the page (Health, Cost, API, Solar) re-renders fresh from the latest data on every refresh.

Split out from #4288, which originally bundled this with two unrelated fixes.

Changes

• apps/predbat/web_metrics_dashboard.py: the afterDraw plugin now reads chart.data.datasets[0].data[0] for the percentage (already correctly updated by mdUpdateSOCChart) and the MD_DATA global for the kWh figures (already correctly reassigned on every refresh), instead of the stale closed-over values.
• apps/predbat/tests/test_metrics_dashboard_soc_refresh.py: no JS execution/browser test infra exists in this codebase, so this checks the generated JS source itself reads from chart.data/MD_DATA rather than the closure parameters, to catch a regression back to the same bug shape.

Test plan

• ./run_all --test metrics_dashboard_soc_refresh - new test passes
• ./run_all --quick - full quick suite passes (611 tests, 0 failures)
• ./run_pre_commit - clean (ruff, black, cspell, markdownlint)

🤖 Implemented with Claude Code, disclosed per repo convention.

[Copilot]

Pull request overview

Fixes the Metrics Dashboard battery SoC doughnut chart center text not updating on periodic refresh by removing stale closure-captured values in the Chart.js afterDraw plugin and instead reading live values from the chart dataset and current MD_DATA. Adds a regression test that inspects the generated JS source to ensure the live-data reads are present, and wires the test into the unit test runner.

Changes:

• Update the Chart.js afterDraw plugin to read the live percentage from chart.data.datasets[0].data[0] and kWh figures from MD_DATA.
• Add a unit test that validates the generated dashboard JS references live data sources (rather than closure variables).
• Register the new test in apps/predbat/unit_test.py.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
apps/predbat/web_metrics_dashboard.py	Updates the SoC chart center-text drawing logic to read live values on refresh.
apps/predbat/unit_test.py	Registers the new metrics-dashboard SoC refresh regression test.
apps/predbat/tests/test_metrics_dashboard_soc_refresh.py	Adds a source-based regression test to prevent reintroducing the stale-closure bug shape.