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>

blog/ogimage.go

@@ -0,0 +1,167 @@
+package blog
+
+import (
+	"bytes"
+	_ "embed"
+	"image"
+	"image/png"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/fogleman/gg"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+)
+
+//go:embed assets/OpenSans-Bold.ttf
+var fontBoldBytes []byte
+
+//go:embed assets/OpenSans-Regular.ttf
+var fontRegularBytes []byte
+
+//go:embed assets/og-base.png
+var ogBaseImage []byte
+
+var (
+	fontBoldParsed    *truetype.Font
+	fontRegularParsed *truetype.Font
+)
+
+func init() {
+	fontBoldParsed, _ = truetype.Parse(fontBoldBytes)
+	fontRegularParsed, _ = truetype.Parse(fontRegularBytes)
+}
+
+func makeFace(f *truetype.Font, size float64) font.Face {
+	return truetype.NewFace(f, &truetype.Options{
+		Size:    size,
+		DPI:     72,
+		Hinting: font.HintingFull,
+	})
+}
+
+// Layout constants — adjust these to reposition text
+const (
+	ogW = 1200
+	ogH = 630
+
+	// Text section (left side)
+	textX      = 60  // left padding for title/description
+	textW      = 680 // max text width for wrapping
+	textStartY = 195 // top of title block
+	lineGap    = 12  // gap between title and description
+
+	// Art section (right side) — domain and date centered here
+	artStartX = 770 // left edge of art section
+	artCX     = 985 // horizontal center of art section (770 + 430/2)
+	domainX   = 1080
+	dateX     = 1100
+	domainY   = 590 // domain text Y
+	dateY     = 30  // date text Y
+
+	titleFontSize  = 56
+	descFontSize   = 26
+	domainFontSize = 22
+	maxTitleLines  = 3
+	maxDescLines   = 5
+)
+
+func ensureGeneratedOGImage(dir, slug, title, dateStr, description string) string {
+	outPath := filepath.Join(dir, slug+".png")
+
+	if _, err := os.Stat(outPath); err == nil {
+		return outPath
+	}
+
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return ""
+	}
+
+	img := generateOGImage(title, dateStr, description)
+
+	f, err := os.Create(outPath)
+	if err != nil {
+		return ""
+	}
+	defer f.Close()
+	png.Encode(f, img)
+
+	return outPath
+}
+
+func generateOGImage(title, dateStr, description string) image.Image {
+	// Decode the embedded base image
+	baseImg, _, _ := image.Decode(bytes.NewReader(ogBaseImage))
+	dc := gg.NewContext(ogW, ogH)
+	dc.DrawImage(baseImg, 0, 0)
+
+	// Domain name — centered in right art section, top
+	dc.SetFontFace(makeFace(fontRegularParsed, domainFontSize))
+	dc.SetRGBA(0.663, 0.639, 0.769, 0.8)
+	dc.DrawStringAnchored("chaosmith.systems", float64(domainX), float64(domainY), 0.5, 0.9)
+
+	// Date — centered in right art section, bottom
+	if dateStr != "" {
+		dc.SetRGBA(0.663, 0.639, 0.769, 0.6)
+		dc.DrawStringAnchored(dateStr, float64(dateX), float64(dateY), 0.5, 0.9)
+	}
+
+	// Title — right section, top-aligned
+	dc.SetFontFace(makeFace(fontBoldParsed, titleFontSize))
+	dc.SetRGB(0.953, 0.941, 1.0)
+
+	titleLines := wrapText(dc, title, float64(textW), maxTitleLines)
+	currY := float64(textStartY)
+	lineH := titleFontSize * 1.2
+	for _, line := range titleLines {
+		dc.DrawStringAnchored(line, float64(textX), currY, 0, 0.5)
+		currY += lineH
+	}
+
+	// Description — below title
+	currY += float64(lineGap)
+	dc.SetFontFace(makeFace(fontRegularParsed, descFontSize))
+	dc.SetRGBA(0.663, 0.639, 0.769, 0.8)
+
+	descLines := wrapText(dc, description, float64(textW), maxDescLines)
+	descLineH := descFontSize * 1.3
+	for _, line := range descLines {
+		dc.DrawStringAnchored(line, float64(textX), currY, 0, 0.5)
+		currY += descLineH
+	}
+
+	return dc.Image()
+}
+
+func wrapText(dc *gg.Context, text string, maxW float64, maxLines int) []string {
+	words := strings.Fields(text)
+	if len(words) == 0 {
+		return []string{""}
+	}
+
+	var lines []string
+	curr := words[0]
+	for _, w := range words[1:] {
+		test := curr + " " + w
+		width, _ := dc.MeasureString(test)
+		if width > maxW {
+			lines = append(lines, curr)
+			curr = w
+		} else {
+			curr = test
+		}
+	}
+	lines = append(lines, curr)
+
+	if len(lines) > maxLines {
+		lines = lines[:maxLines]
+		last := lines[maxLines-1]
+		if len(last) > 3 {
+			last = last[:len(last)-3] + "..."
+		}
+		lines[maxLines-1] = last
+	}
+
+	return lines
+}