fix(web): add aria-label to file-tab icon-only toolbar buttons

[pedrofrxncx]

Source: bug found while sweeping apps/web/src for accessibility gaps in the main-panel-tabs directory.

Payoff: the three toolbar buttons in FileTab (download / open-in-new-tab / close) are icon-only with a Radix Tooltip but no aria-label. Radix's tooltip wiring only adds aria-describedby (a supplementary description), not an accessible name, so screen readers announce these as unlabeled "button" — same class of bug fixed in #4903, #5047, #5096, #5226, #5271, #5385, #5412. The sibling file code-tab.tsx already follows the correct aria-label pattern for its icon-only IDE-launch buttons, confirming file-tab.tsx was simply missed.

Fix: added aria-label={t(...)} to each of the three buttons, reusing the existing translation strings already used in the adjacent TooltipContent (mainPanelTabs.fileTab.download / .openInNewTab / .close) — no new i18n keys needed, no behavior change.

Verify: open a thread with a file output, tab into the file preview toolbar with a screen reader (or inspect the accessibility tree) and confirm each icon button now announces its action.

Checks run locally: bun run fmt (clean), bunx tsc --noEmit in apps/web (clean). No test file covers this component; full CI validates the rest.

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Summary by cubic

Adds aria-labels to the three icon-only buttons in the FileTab toolbar so screen readers announce their actions; reuses existing i18n strings with no UI or behavior changes.

• Bug Fixes
  • Added aria-labels to Download, Open in new tab, and Close buttons using existing mainPanelTabs.fileTab.* translations.
  • Resolves unlabeled “button” announcements; tooltips alone were not providing accessible names.

^{Written for commit 9eda91e. Summary will update on new commits.}