feat: add confetti animation on game win

[DaniilSyzenko]

Adds a confetti celebration animation on game win when the GameSummaryScreen loads.

• Confetti fires when GameSummaryScreen mounts
• Uses white and gold colours to match the app colour palette
• Stops playing after 3 seconds
• Doesn't play again until another win

Fixes #5

[BySplashGm]

Great contribution overall — the widget lifecycle handling, dispose, and the custom star shape are all well done.

One visual bug to fix before merging: the stars accumulate at the emission point rather than spreading across the screen. Two things causing this:

• blastDirectionality: BlastDirectionality.explosive and blastDirection: -pi / 2 conflict — in explosive mode the blast direction is ignored. Pick one: either explosive (all directions) or directional with your -pi / 2 angle
• gravity: 0.05 is very low, so particles float in place instead of falling — try something around 0.2–0.3

A directional upward fountain from the center with higher gravity should give a clean result.

[DaniilSyzenko]

Hi, can I still work on this?

[BySplashGm]

sure! i'll reopen your PR