chore: add Biome and document design decisions from grill session

- Add @biomejs/biome 2.5.3 with 2-space indent, double quotes, trailing commas
- Add lint and format scripts to root package.json
- Update CONTEXT.md: resolve Structured Output shape, add Document AST, Block, Inline Node terms
- Add ADR 0002 (remark as internal Markdown parser)
- Add ADR 0003 (core defines own AST types)
- Add spec: core-parser (Parser implementation and Document AST)
- Add spec: cli-view (kitchen view <file> command)

package.json

@@ -2,11 +2,17 @@
   "name": "kitchen-md",
   "version": "0.0.0",
   "private": true,
-  "workspaces": ["packages/core", "packages/bin"],
+  "workspaces": [
+    "packages/core",
+    "packages/bin"
+  ],
   "scripts": {
-    "test": "bun test"
+    "test": "bun test",
+    "lint": "biome check .",
+    "format": "biome check --write ."
   },
   "devDependencies": {
+    "@biomejs/biome": "^2.5.3",
     "bun-types": "latest"
   }
 }