fix: ms exact mass (M+)

[Nicolass67]

Summary

• show Exact mass (M+) instead of neutral M in the MS info panel
• calculate the displayed value by subtracting the electron mass from the exact mass
• add a focused test for the M to M+ conversion

Test plan

• open an MS spectrum and check that the info panel shows Exact mass (M+)
• verify the displayed value is slightly lower than the neutral exact mass
• run the InfoPanel test

[Copilot]

Pull request overview

Updates the MS info panel to display the charged-species exact mass (M+) rather than the neutral exact mass, aligning the UI with typical MS reporting by subtracting the electron mass, and adds a focused unit test to validate the conversion.

Changes:

• Add MS-specific exact mass formatting that converts neutral mass M to M+ by subtracting electron mass and formatting to 6 decimals.
• Update the InfoPanel label to Exact mass (M+) and display the converted value.
• Add a unit test asserting the displayed M+ value for MS layout.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/components/panel/info.js	Introduces M→M+ conversion for MS layout and updates the displayed label/value in the InfoPanel.
src/__tests__/units/components/panel/info.test.js	Adds a unit test verifying the M+ exact mass display for MS layout.

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