[Everton (evertonrocha2)]

Description

Closes #3726.

Adds eslint-plugin-jsx-a11y to the frontend lint and makes its recommended rules blocking for production components (src/**/*.tsx, tests excluded). I triaged the 25 findings on current main:

Fixed (1)

• The ConverterPanel resize handle only worked with a mouse. It's now a focusable role="separator" (WAI-ARIA window splitter): Left/Right resize by 16px, Home/End jump to the min/max width, and aria-valuenow/min/max expose the current width.

Handled in config (9)

• no-noninteractive-tabindex also allows role="region" and role="separator", so labelled scroll regions (3) and the new splitter can take focus.
• media-has-caption is off (6). Every <audio>/<video> here renders user-supplied attack content or target output, so there's no caption track to provide.

Inline disables, each with a reason (15 findings, 14 comments)

• Tooltip wrappers around disabled controls (6) and a scorer metric value (1). A disabled Fluent control can't take focus, so the wrapper is focusable to let keyboard users reach the tooltip.
• Two more scroll containers (a <section> and a <pre>) that need focus to scroll with the keyboard.
• LabelsBar (2 elements, 4 findings). The pill's click handler only catches clicks on its own padding. The inner edit control already has role="button", tabIndex and onKeyDown.
• ObjectiveHeader autoFocus: focus moves into the inline editor the user just opened.
• TechniqueEditor: the onKeyDown only keeps Enter in a field from submitting the form.
• ConverterPanel separator: jsx-a11y treats separator as non-interactive even when it's focusable (jsx-a11y/eslint-plugin-jsx-a11y#577).

Lint already runs with --report-unused-disable-directives, so a stale disable will fail CI too.

Notes

• eslint-plugin-jsx-a11y 6.10.2 lists peer deps up to ESLint 9, but it runs fine on ESLint 10, and the repo's .npmrc already sets legacy-peer-deps. Happy to switch to the maintained fork eslint-plugin-jsx-a11y-x if you prefer. It gives the same results here.
• Lockfile: adds the plugin's dependencies. The only existing package that changed is es-object-atoms (1.1.1 to 1.1.2, patch).
• Possible follow-up, not in this PR: the disabled-control wrappers are generic <span>s with aria-label, which some screen readers ignore. Fluent's disabledFocusable on Button could replace most of them.

Tests and Documentation

• New tests in ConverterPanel.test.tsx: the handle is exposed as a focusable separator with its current width, and Arrow/Home/End resize it within bounds.
• npm run lint and tsc --noEmit pass. I also checked that a new <div onClick> in a component now fails lint.
• Tests for every touched component pass. On the full suite, I see the same 3 failures with and without this change. They come from locale-dependent number formatting in analytics tests (my machine is pt-BR).
• No docs changes.

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[Everton (evertonrocha2)]

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