Fix the accessibility findings and enforce the rules

[blakebauman]

Clears the accessibility debt left by #13 and puts the rules back at error severity in biome.json. They were set to warn there only so the findings stayed visible rather than being switched off; this makes them enforced, so regressions fail CI.

Nine real defects

ListItem	Carried role="button" and tabIndex={0} unconditionally, so rows rendered without an onClick — K8sResourcesPage renders them that way — sat in the tab order announcing themselves as controls that did nothing. Now a real <button> when interactive and a plain <div> when not, which also drops the hand-rolled Enter/Space handler for native behaviour.
RowMenu	onClick was attached unconditionally while role, tabIndex and onKeyDown were all gated on selectable — a click target with no keyboard path whenever a row was not selectable.
State filter	A div with role="group" wrapping checkboxes. It is a genuine form-control group, so it is now a <fieldset> with an sr-only <legend>.
LabelChips	aria-label on a bare div, where it is never exposed. The chips are a list, so <ul>/<li>.
Status dots	ConsolePanel and ExecTerminal labelled a dot that duplicates the adjacent status text, so the state was announced twice. Decorative, now aria-hidden.
Four chart SVGs	No accessible name. AreaChart and RingGauge are decorative — the value sits beside them as text — so they are aria-hidden. ChartsPanel and LiveSparkline are the only carriers of their data, so they get role="img" and a <title> stating the series, latest value and peak.

Seven false positives

Suppressed individually with the reason named, rather than switching the rules off:

• The xterm host onClick only forwards stray clicks on the padding; keyboard users reach the terminal through xterm's own textarea, already in the tab order.
• RowMenu's two inner wrappers exist solely to stop the row click reaching their children — the checkbox and menu trigger are the real controls — and the outer row's four selectable ternaries cannot be correlated by the rule.
• SegmentedControl and the sidebar mode switcher are button groups, which is ARIA role="group". useSemanticElements suggests <fieldset>, which is for grouping form controls and would be wrong here.

RowMenu and SegmentedControl use file-level biome-ignore-all because the flagged element is the root of a return, where a JSX comment cannot precede it.

Verification

biome ci passes with the a11y rules at error, plus tsc --noEmit and the production build.

Checked in the browser against a live engine, since three of these change DOM structure and could shift layout: the <fieldset> renders with no default border or padding, the label chips wrap with no list bullets or indentation, row selection and the detail panes still work, and the sparklines render.

Not verified: the ListItem change on K8sResourcesPage, as no cluster was reachable. It compiles and typechecks, and that consumer passes no onClick, so it takes the plain-div branch.

🤖 Generated with Claude Code

https://claude.ai/code/session_015dD6k7ZHtNg7d44xnKLMjH