Route a source's content to the layout that fits it

[davertor]

TLDR: A note's layout now comes from what the source is, not from one fixed shape. A comparison of tools renders as a field guide with a matrix and a card per entry; a dish renders as a recipe card; everything else stays the annotated offprint.

• A genre is a body contract plus a template. SKILL.md Step 3 classifies the source after reading it — top to bottom, first row that fits — and reads that genre's contract, which replaces ## Sections and nothing else. When the call is not obvious it stays offprint: a wrong genre is worse than the plain one. --genre or a request in words overrides it.
• fieldguide — for several things of one kind on shared axes. Full-bleed masthead, a cost matrix, a <section class="entry"> per thing with the same facets, and up to three picks. Contract in genres/fieldguide.md.
• recipe — a ticket of facts lifted into the masthead, the ingredients pinned in a rail beside the method, numbered steps carrying their time and setting. A video recipe's steps link to the minute. Contract in genres/recipe.md.
• One template per genre, resolving video vs article inside — only the masthead differs (poster or byline kicker), so notes.py reads a genre note back with the same parser and retag.py finds the same anchor.
• kind and genre are separate axes. kind (video/article) still comes from --video-id; genre is declared as data-genre on <html>, absent meaning offprint — so every note written before this parses as one. The gallery labels the genre beside the kind and makes it searchable; Markdown export carries it in the frontmatter.
• The genre templates consume the palette tokens and hard-code no colour, so every theme works in every layout.
• Contracts forbid <article> inside the body: the parser ends the note at the first </article>, which would have silently truncated a field guide after its first entry.

Builds on #8.