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>

.pre-commit-config.yaml

@@ -7,7 +7,7 @@ repos:
       - id: check-yaml
       - id: check-json
       - id: check-added-large-files
-        args: ['--maxkb=500']
+        args: ["--maxkb=500"]
       - id: check-merge-conflict
 
   - repo: https://github.com/psf/black
@@ -22,3 +22,9 @@ repos:
     hooks:
       - id: isort
         args: [--settings-path=pyproject.toml]
+
+  - repo: https://github.com/pre-commit/mirrors-prettier
+    rev: v4.0.0-alpha.8
+    hooks:
+      - id: prettier
+        exclude: ^(dist/|package-lock\.json|\.venv/|python/)