Styling and formatting: shared asset bundle, leaderboard improvements, translated stage badges

[kilgor-trout-c22]

What

Styling and formatting improvements across the module, one commit per topic:

• Shared asset bundle — the front-end styles move from inline CSS on the competition view into an asset bundle loaded on every Kickoff page. Fixes the rules/leaderboard pages rendering unstyled when opened directly (e.g. right-click → open in new tab), and banner buttons sticking in their "active" state after such navigation (:focus-visible instead of :focus).
• Standard table heads — tables across the module adopt HumHub's standard table-head styling for a consistent look with the rest of the admin UI.
• Profile pictures on leaderboards — the leaderboard page and the competition view's Top 10 show each player's picture next to their name (HumHub's standard user image); the tip-history popup shows it in its header.
• Tendency column + tiebreakers — leaderboards show a count for every scoring tier (Total / Exact / Goal diff / Tendency) with explanatory tooltips. Ties break by total points, then exact hits, then goal differences, then tendencies. Column widths balanced via table-layout: fixed.
• Translated stage badges — knockout match cards show "Semi-finals" / "Halbfinale" instead of internal slugs (semi), sharing one label source (Game::stageLabel()) with the matchday dropdown.