Adds the player's home planet to the starting system, rendered from the new
planets.png spritesheet. The planet is a solid disc: the ship may come within
shipClearance of its rim but can never cross it, and clicks on the planet
clamp to the keep-out rim so the ship always has a reachable destination.
- js/entities/Planet.js: solid-disc entity with a circle keep-out constraint
(constrainShip/resolve, pure and scene-free) plus edgePoint/aimPoint helpers
- data/planets.json (+ manifest entry): texture, frame size, scale, homePlanet,
shipClearance, spawnDistanceFromEdge
- Ship.js: exposes a radius (half the hull width) for the keep-out math
- GameScene.js: loads the spritesheet, spawns the home world at the origin,
starts the ship ~150 px off its rim in a seed-derived direction, and applies
the constraint each frame after the ship moves
- dev/planet.test.mjs: Node tests of the constraint against real config;
dev/test-game.html gains a <base href> so asset paths resolve from /dev