fix: accessibility pass — keyboard reachability and dialog semantics

[NovakPAai]

Summary

Follow-up on a UX audit run across Overview, Projects, Sessions, and Workspace: keyboard/screen-reader support was inconsistent throughout — some controls had real focus/ARIA semantics, most didn't. This closes the accessibility gaps found (see conversation history for the full audit).

• Overview: .ov-card gets a visible :focus-visible outline (it was already a real <button>, just missing the ring — every other button class in the app has one).
• Calendar: day cells are now real <button>s (were unfocusable <div>s) with aria-pressed reflecting selection; the popup is a proper role="dialog" aria-modal with Escape-to-close and focus returned to the date button on close.
• Add Project modal: addProjectSwitchTab() now updates aria-selected/roving tabindex when switching tabs — it previously only toggled the visual .active class, so a screen reader kept announcing the first tab as selected forever. Added Left/Right/Home/End arrow-key navigation matching the existing Projects/History tablist pattern one function away.
• Session cards (.card / .list-row / .qa-item): were plain <div>s with an onclick and nested buttons — entirely unreachable by Tab, only mouse or the undiscoverable j/k shortcuts worked. Added tabindex, a descriptive aria-label, :focus-visible styling, and a shared onCardKeydown handler (Enter/Space triggers the card's own click, guarded so it doesn't also double-fire for a nested button/checkbox's own key handling).
• Detail panel: role="dialog" aria-modal, wired into the existing _installModalFocusTrap/_uninstallModalFocusTrap helper (same one Add Project / Projects Settings already use) for Tab-trapping and focus-return on close. Also hardened _uninstallModalFocusTrap to skip focus-return when the captured element has since been detached from the DOM (a background poll/re-render can replace it while a modal is open) instead of silently stranding focus on the modal's own now-hidden close button.
• Workspace: aria-label on the pane close button, tab close button, and the three launch/layout <select> menus that only had a title before. Split-pane resize handles (.ws-resizer) are now real ARIA separators — tabindex, role="separator", aria-orientation, and arrow-key resize (mirrors the pointer-drag math without triggering a full handle rebuild mid-interaction, which would destroy and unfocus the handle the user is actively adjusting).

Test plan

• node --test "test/**/*.test.js" — 257 passed, 1 skipped (win32-only)
• Verified live in a browser (Playwright): Tab reaches a session card, Enter opens the detail dialog with focus auto-landed on the close button; Escape closes it and returns focus to the originating card; calendar popup opens as a dialog, Escape closes and returns focus to the date button; Add Project tabs correctly sync aria-selected/tabindex on click and via arrow-key navigation

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