Add tetris example

tetris/proposal.md

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+## Game name
+
+Tessera
+
+## Vision
+
+Tessera takes classic Tetris and adds a light puzzle layer: arranged clears that match colors grant small bonuses, rewarding planning without changing the tight, fast arcade feel. It's worth making because it blends a familiar, addictive core with a gentle twist that increases depth for skilled players while staying approachable.
+
+## What the game will look like
+
+A clean, modern pixel/flat aesthetic with bright, readable tetromino colors on a dark background; the HUD shows next pieces, hold slot, score, level, and subtle particle effects on clears.
+
+## Player interaction
+
+Players use keyboard controls to move, rotate, soft/hard drop, and hold pieces; menus use simple mouse/keyboard navigation. The game emphasizes quick decision-making and responsive controls with a visible ghost piece to aid placement.
+
+## Core mechanics
+
+1. Falling tetromino placement and rotation — move and rotate pieces to fit them into the well.
+2. Line clearing and gravity — completed rows clear and the above rows shift down, possibly chaining combos.
+3. Hold and next-queue — store one piece and preview upcoming pieces to plan ahead.
+4. Color-match bonus (optional) — clearing lines where most blocks share a color grants small score/energy bonuses to encourage pattern play.
+
+## Milestone (first target)
+
+Implement the core game engine: represent the board and pieces, support spawning, movement, rotation, collision detection, locking, and single-line clearing so you can run a minimal playable loop and unit tests for the engine.
+