UPDATABLE FIELDS (grouped by section):

                TOP-LEVEL:
                - long_description: Company marketing description
                - logo_url / logo_urls: Direct URL(s) to logo images (permanent override; super-user only)
                - clear_logos: true removes the permanent logo override (super-user only)
                - search_keywords: List of SEO/search keywords
                - colors: Legacy flat color list [{hex, type, name?}]
                - fonts: Legacy flat font list [{name, type}]
                - website_background: Hex color of the brand website's background, used by generate_brand_creative as the default ad background

                COLOR PALETTES (each entry: {hex, name, usage}):
                - primary_colors, secondary_colors, accent_colors, extended_palette, semantic_colors

                TYPOGRAPHY (string values):
                Layered creatives set the headline in headline_font and the supporting line,
                the CTA and any other text in body_font (primary_font only where those are
                unset). To put a font in layered creatives, set headline_font and/or
                body_font: they do not read secondary_font, eyebrow_font, subtitle_font,
                cta_font or the legacy fonts list. They load their hosted fonts and Google
                Fonts families only. A headline_font, body_font or primary_font they
                cannot load is not saved when it is a near miss of one of their hosted
                fonts or a common Google Fonts family, or when its title-cased spelling
                is a Google Fonts family (lato for Lato); the result names the family to
                use instead. Any other name they cannot load is saved, and the result
                says which font they use in its place.
                - primary_font, primary_font_usage, secondary_font, secondary_font_usage
                - headline_font, headline_weight, headline_size, headline_case, headline_linespace, headline_letterspace
                - eyebrow_font, eyebrow_weight, eyebrow_case, eyebrow_linespace, eyebrow_letterspace
                - subtitle_font, subtitle_weight, subtitle_linespace, subtitle_letterspace
                - body_font, body_weight, body_size, body_linespace, body_letterspace
                - cta_font, cta_weight, cta_size, cta_linespace, cta_letterspace

                LOGO USAGE:
                - logo_on_dark, logo_on_light, logo_clear_space: string rules
                - logo_misuse: list of misuse rules

                CTA SYSTEM:
                - button_shape, button_background, button_text_color, button_text_weight, button_text_case, button_padding
                - standard_ctas: list of CTA labels
                - cta_placement: placement guidance

                SIGNATURE ELEMENTS:
                - tagline, tagline_placement: strings
                - tagline_variants, visual_motifs, promotional_elements: lists

                MESSAGING:
                - tone: string
                - value_propositions, headline_formulas, proof_points: lists
                - product_names: dict (e.g. {platform: "X", vlm: "Y"})

                CONTENT HIERARCHY:
                - content_hierarchy_order: list, content_hierarchy_spacing: string, content_hierarchy_text_max_width: string

                PHOTOGRAPHY:
                - photography_style, photography_treatment, photography_avoid: strings
                - photography_subjects: list

                RULES:
                - dos: list of "do" rules
                - donts: list of "don't" rules

                LAYOUT & CHANNELS:
                - primary_layouts: list of layout dicts
                - channel_linkedin, channel_facebook, channel_display: channel config dicts

                EXAMPLE: {"company_url": "ambient.ai", "tagline": "See what matters.", "headline_font": "Chakra Petch", "primary_colors": [{"hex": "#FFFFFF", "name": "White", "usage": "Primary background"}]}