app/vmui: fix rendering of the first bar overlapping the start of the range

[Loori-R]

Describe Your Changes

Fixes bar chart rendering at the start of the selected time range.
If the first bar starts before start but ends within the selected range, it is now included and rendered instead of being skipped.

Before
After

Checklist

The following checks are mandatory:

• My change adheres to VictoriaMetrics contributing guidelines.
• My change adheres to VictoriaMetrics development goals.

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Summary by cubic

Fixes missing first bar in HitsChart when it starts before the selected range but ends within it. This removes gaps at the start of the chart.

• Bug Fixes
  • Build the x-axis from unique hit timestamps instead of step-based generation to include overlapping bars at the range start.
  • Removed barsCount/useHitsChartConfig/getHitsTimeParams and simplified timestamp logic.
  • Updated changelog with the web UI bugfix.

^{Written for commit 71d41af. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

[arturminchukov]

LGTM!

[valyala]

@Loori-R , thank you for the fix!