Add design system, audit sections, apply global classes

Design system (design/):
- bcw-css-variables.json: color, spacing (--space-xs→2xl), typography (--h1→h6, --text-sm→xl)
- bcw-color-palette.json: named swatches referencing CSS variables
- bcw-global-classes.json: section-container, section-header, col-3, col-4, features-container, footer-sub-section
- design.md: full variable reference and usage guide

Templates:
- features-3col + features-4col: add global_classes embed + _cssGlobalClasses references
- All headers + footers: apply var(--color-primary) background to section elements
- footer-columns: add footer-sub-section class to column containers
- Remove content-image-left (duplicate of content-image-right with children reversed)
- testimonials: gap tweak 12px → 15px on card containers

Repo hygiene:
- Add .gitignore (Updated_Sections/)
- Clear Updated_Sections staging folder

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

TODO.md

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+TODO:
+
+- Updated sections with updated sections found at ./Updated_Sections
+- Institute some Global CSS Variables for color (Primary, Secondary, Tertiary)
+  - Assign primary color as background for header & footer
+  - Assign colors throughout the site
+    - Maybe make an importable theme style for Bricks?
+- Also build a Global Classes import sheet, for sharing classes between 3 row containers, 4 row containers, footer sub section containers, etc.