fix(dashboard): UX/a11y/perf/correctness pass

[iammukeshm]

What

A focused UX / accessibility / performance / correctness pass over the tenant dashboard (clients/dashboard), driven by a four-dimension audit. No backend or src/BuildingBlocks changes.

Why

The dashboard was already mature, so this targets the things lint can't catch: silent realtime bugs, invalid ARIA, contrast gaps, and a few dead-code / footgun spots.

Highlights

Functional bugs

• 4 hub events subscribed but never wired in realtime-context.tsx (PresenceChanged, ChatMessagePinned, ChatMessageUnpinned, ChatChannelMemberRead) — live presence dots, pin/unpin, and read-receipts silently never updated. The backend broadcasts all four.
• chat-search highlight: a /g RegExp.test() in a .map() drifted lastIndex and mis-wrapped matches.
• user-detail: the staged-role reset was keyed on roles = data ?? [], so a background refetch could wipe unsaved edits — re-keyed on userId with a deterministic post-save clear.

Accessibility

• Combobox: invalid role="option" inside a role="menu" and role="combobox" without aria-expanded/controls → valid menuitemradio; nested interactive clear button lifted to a sibling.
• Accessible names: reaction chips, quick-react emoji, EntitySearch (every list page), collapsed sidebar items.
• role="status"/sr-only on skeletons, role="progressbar" on upload bars, DialogTitle on the mobile nav Sheet, anchor-as-menuitem (asChild) for link menu items, h1→h2 heading hierarchy, chat status rows hidden from the role="log" region.
• Placeholder contrast raised to AA (removed sub-AA alpha multipliers).

UX / correctness

• Retired hardcoded text-white/bg-white/bg-black via a new theme-independent --color-overlay-foreground / --color-overlay token + semantic foregrounds.
• Profile form: surfaces load errors, gates inputs while loading, seeds once (no clobber on refetch).
• Wired the previously no-op "Reduce motion" toggle through the theme provider (persisted + .reduce-motion class + CSS); fixed the notifications "open bell" selector.

Cleanup

• Removed 3 void X dead-import hacks + a dead effect, swapped a full-page window.location reload for router navigate(), and resolved all 10 exhaustive-deps lint warnings via useMemo.

Deliberately deferred

• Global token-syntax normalization and products.tsx primitive de-dup (render identically — churn without a defect).
• Server-side pagination for roles/groups at scale and a batched presence endpoint (need API changes).
• The 12 remaining lint warnings are all pre-existing react-refresh/only-export-components (dev-only HMR ergonomics).

Verification

• tsc -b clean
• eslint 0 errors, 12 warnings (down from 22)
• vite build succeeds
• Playwright 121/121 pass (updated 3 identity empty-state heading-level assertions to match the corrected h2)

Note (golden rule #10): the now-working reduce-motion toggle and live-presence fix are user-facing — a changelog entry in the separate docs repo should accompany this before release.

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