Clean up podcast social image generation

[mre]

Summary

• remove the large Rust Foundation-specific social image render path
• make social image generation use bundled fonts consistently instead of ImageMagick font names
• instantiate a real Inter Bold from InterVariable.woff2 for normal post captions so blog cards keep their previous bold look
• split long podcast bylines automatically when they exceed the safe width
• render podcast logos on transparent backgrounds before recoloring, avoiding filled logo tiles
• regenerate all social images with the bundled-font stack
• skip generated target directories while walking content

Notes

• requires woff2_decompress to be available when running scripts/social.sh
• requires fonttools to instantiate the bundled Inter Bold font for normal post captions

Validation

• bash -n scripts/social.sh
• ./scripts/social.sh --force
• compared content/blog/async/social.png against upstream/master; static Inter Bold is much closer to the old render than the variable-font weight path
• visually inspected content/podcast/s06e08-rust-foundation/social.png
• visually inspected content/podcast/s06e06-clickhouse/social.png
• visually inspected content/blog/async/social.png