refactor: codebase audit — remove orphaned blocks, unify design tokens
- Delete 5 orphaned blocks: ArchiveBlock, CallToAction, Content, Form, RelatedPosts
- Remove Form import from RenderBlocks
- Delete Media-BACKUP.txt
- Extract fdCardRadius, fdCardRadiusSm to fdTheme — adopted across 15 blocks
- Extract fdContainer to fdTheme — adopted across 29 blocks
- Add fdSepiaOverlay, fd-sepia CSS token — replaces hardcoded #8B7D3C
- Replace #153350 with via-fd-navy-700 in navyGradient
- Replace #e2e8f0 with fd-gray-light in calculator blocks
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