fix: resolve historical reaction names in tooltips

[MohamadJaara]

Summary

• Keep the inline reaction count based on every stored reactor ID, including users who left the conversation.
• Keep cached current conversation members as the immediate source for tooltip names.
• Resolve missing tooltip-visible reactor names from IndexedDB only when the tooltip opens.

Behavior

• No IndexedDB lookup occurs while the message list renders.
• A lookup is triggered only by the hover or focus interaction that opens the tooltip.
• Only reactor IDs missing from the cached conversation members are requested.
• Only the first two reactors whose names can appear in the tooltip are considered; missing users represented by the remaining count are not loaded.
• The lookup is local-only and never requests the backend.
• If a user is not available in IndexedDB, the tooltip shows the translated deleted-user label instead of an undefined name.

Validation

• yarn type-check
• BASE_REF=main yarn lint:affected
• Reaction tooltip regression tests
• Content message and message wrapper tests
• User repository local-only lookup test

Follow-up to #22251.