FA tab badge, 0-10 Fantasy Score caption, and refreshed README GIFs

[YonatanHen]

Summary

• Tab badge (favicon): frontend/public/favicon.svg has a green F (accent #34d98c) and a white A on the app's dark background (#0a0f0d). It is linked from index.html. The letters are drawn as shapes, so they do not depend on fonts. It also fixes the favicon.ico 404 in the browser console.
• Player page caption: the subtitle showed the old formula. It now shows Fantasy Score (0-10) = (raw/90 × starter + playing-time bonus) × confidence.
• README GIFs: re-recorded 01-player-details, 02-player-modal, 03-compare and 04-xgi-outliers with the 0-10 Fantasy Score, the 0-10 bars and the 0-10 pillar scores (PR Chat model fallback, per-league chat answers, and Fantasy Score in a strict 0-10 range #36). Each is cropped to 1398×632 and is 0.45-1.5 MB. The first two README captions now mention the 0-10 scale. 05-scatter-plot and 06-ask-ai-chat are not changed.

Test plan

• ruff check, ruff format --check, pytest: 364 passed, 7 skipped (no backend change)
• tsc --noEmit and eslint src: clean
• The favicon is served as image/svg+xml. Checked visually at 128, 32 and 16 px on light and dark tab bars.

Merged without waiting for CI, at the user's request.

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