Add article of 2025-12-09

Author: actions-user

docs/2025/puzzles/day09.md

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+import Solver from "../../../../../website/src/components/Solver.js"
+
+# Day 9: Movie Theater
+
+## Puzzle description
+
+https://adventofcode.com/2025/day/9
+
+## Solutions from the community
+
+Share your solution to the Scala community by editing this page.
+You can even write the whole article! [Go here to volunteer](https://github.com/scalacenter/scala-advent-of-code/discussions/842)