style: apply Prettier formatting to TS/JS/JSON/MD files

Add Prettier as a dev dependency with .prettierrc.json config and
.prettierignore. Hook added via mirrors-prettier in pre-commit config.
All TypeScript, JSON, Markdown, and YAML files auto-formatted.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tsconfig.json

@@ -1,14 +1,14 @@
-{
-  "compilerOptions": {
-    "target": "ES2020",
-    "module": "NodeNext",
-    "moduleResolution": "NodeNext",
-    "esModuleInterop": true,
-    "strict": true,
-    "outDir": "dist",
-    "declaration": true,
-    "sourceMap": true
-  },
-  "include": ["src/**/*"],
-  "exclude": ["node_modules", "dist"]
-}
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "esModuleInterop": true,
+    "strict": true,
+    "outDir": "dist",
+    "declaration": true,
+    "sourceMap": true
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}