Configure Prettier and ESLint base

Prettier: no semicolons, single quotes, no trailing commas, 100-column
body width, 80-column prose markdown. Svelte plugin registered for
component formatting.

ESLint is added in a separate commit since the lint rule forbidding
Math.random in gameplay code is its load-bearing purpose; the base
flat config appears there.

2 files changed, 36 insertions, 0 deletions

diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..57c2336
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1,10 @@
+.claude/
+.svelte-kit/
+build/
+dist/
+built/
+node_modules/
+coverage/
+pnpm-lock.yaml
+*.min.js
+*.min.css
diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 0000000..9c197bb
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,26 @@
+{
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "none",
+  "printWidth": 100,
+  "tabWidth": 2,
+  "useTabs": false,
+  "arrowParens": "always",
+  "endOfLine": "lf",
+  "plugins": ["prettier-plugin-svelte"],
+  "overrides": [
+    {
+      "files": "*.svelte",
+      "options": {
+        "parser": "svelte"
+      }
+    },
+    {
+      "files": "*.md",
+      "options": {
+        "printWidth": 80,
+        "proseWrap": "preserve"
+      }
+    }
+  ]
+}