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)

.claude/CONTEXT.md

@@ -103,12 +103,34 @@ It is a pure function of its input string — no filesystem access.
 
 ## Structured Output
 
-The data object returned by the Parser for a given Recipe File.
-Shape is not yet fully specified — see open questions below.
+The Document AST returned by the Parser for a given Recipe File.
+See **Document AST** for the exact shape.
+
+## Document AST
+
+The full structured representation of a Recipe File returned by the Parser.
+Top-level shape: `{ frontmatter: Record<string, unknown>, blocks: Block[] }`.
+`frontmatter` is the raw YAML metadata, passed through without schema enforcement.
+`blocks` is a flat, ordered list of Block nodes representing the document body in document order.
+The flat structure means headings and their following content are siblings, not parent/child.
+Consumers that need section grouping derive it by scanning for Heading nodes.
+Core defines its own AST node types; remark (the internal Markdown parser) is a private implementation detail and its types do not appear in the public API.
+See ADR 0002 and ADR 0003.
+
+## Block
+
+A top-level node in the Document AST's `blocks` array.
+Each Block represents one logical unit of document structure: a heading, a paragraph, a list, a code block, etc.
+Block types are defined by core; the exact catalogue is not yet finalised — see open questions below.
+
+## Inline Node
+
+A node representing inline content within a Block (e.g. within a paragraph or list item).
+Inline nodes include: plain text, emphasis, strong, code span, link, Wikilink, and the three Annotation types (Ingredient, Cookware, Timer).
 
 ---
 
 ## Open / Unresolved
 
-- **Structured Output shape** — exact fields, types, and nesting of the parse result.
+- **Block node type catalogue** — the exact set of Block types core defines (heading, paragraph, list, code block, blockquote, etc.) and how unrecognised types are represented.
 - **Unit normalisation** — the parser should normalise known aliases to a canonical abbreviation (`grams` → `g`, `kilograms` → `kg`); exact alias table and canonical forms are TBD. This is a parser concern, not a format constraint.