feat: OpenGraph metadata + auto-generated OG card images

- Per-post OG tags (title, description, image, date) in template head
- Twitter Card support (summary_large_image)
- Auto-generate 1200x630 card images from embedded base PNG
- Title, description, domain, date drawn on image via fogleman/gg
- Fonts embedded via go:embed (OpenSans Bold + Regular)
- Optional og-image: and og-description: front matter overrides
- Layout constants in ogimage.go for easy repositioning
- Generated images cached in content/og/ (gitignored)

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <noreply@letta.com>

go.mod

@@ -3,3 +3,10 @@ module chaosmith-site
 go 1.26.4
 
 require github.com/yuin/goldmark v1.8.2
+
+require (
+	github.com/fogleman/gg v1.3.0 // indirect
+	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 // indirect
+	golang.org/x/image v0.43.0 // indirect
+	golang.org/x/text v0.38.0 // indirect
+)