bug: Missing empty search state in LeaderboardTable when developer filter yields no results #250

When filtering developers in LeaderboardTable (src/features/leaderboard/components/leaderboard-table.tsx), if no developer matches the search query (filtered.length === 0), the table body renders completely blank (<tbody> has 0 rows). The table headers remain, but there is no feedback or way to clear the filter.

Motivation

When users filter by a name that doesn't exist, a blank table appears broken. Providing an informative empty state with a 1-click 'Clear search' button significantly improves discovery UX.

Tasks

• When filtered.length === 0 && search.trim(), render a full-width <tr><td colSpan={6}>...</td></tr> empty state.
• Display a helpful message: t("leaderboard.noDevelopersSearch", { query: search }).
• Add a small secondary button to clear the search filter (setSearch("")).
• Add translation keys to src/locales/en.json and src/locales/ar.json.

Files to Check

• src/features/leaderboard/components/leaderboard-table.tsx
• src/locales/en.json & src/locales/ar.json