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/store.go

@@ -20,10 +20,13 @@ var md = goldmark.New(
 )
 
 type Post struct {
-	Slug  string
-	Title string
-	Date  time.Time
-	HTML  string
+	Slug          string
+	Title         string
+	Date          time.Time
+	HTML          string
+	Description   string
+	OGImage       string
+	OGImageCustom bool
 }
 
 type Store struct {
@@ -56,19 +59,27 @@ func (s *Store) Load(dir string) error {
 		}
 
 		slug := strings.TrimSuffix(e.Name(), ".md")
-		title, body, date := parseFrontMatter(raw, slug, path)
+		title, body, date, ogImage, ogImageCustom, description := parseFrontMatter(raw, slug, path)
 
 		var buf bytes.Buffer
 		if err := md.Convert(body, &buf); err != nil {
 			continue
 		}
 
+		ogImagePath := ogImage
+		if !ogImageCustom {
+			ogImagePath = "/blog/og/" + slug + ".png"
+		}
+
 		s.index[slug] = len(s.posts)
 		s.posts = append(s.posts, Post{
-			Slug:  slug,
-			Title: title,
-			Date:  date,
-			HTML:  buf.String(),
+			Slug:          slug,
+			Title:         title,
+			Date:          date,
+			HTML:          buf.String(),
+			Description:   description,
+			OGImage:       ogImagePath,
+			OGImageCustom: ogImageCustom,
 		})
 	}
 
@@ -83,6 +94,15 @@ func (s *Store) Load(dir string) error {
 	return nil
 }
 
+func (s *Store) GenerateOGImages(dir string) {
+	for _, p := range s.posts {
+		if p.OGImageCustom {
+			continue
+		}
+		ensureGeneratedOGImage(dir, p.Slug, p.Title, p.Date.Format("January 2, 2006"), p.Description)
+	}
+}
+
 func (s *Store) All() []Post {
 	return s.posts
 }
@@ -112,7 +132,8 @@ var dateFormats = []string{
 // parseFrontMatter extracts the title from the first `# heading`,
 // strips that line from the body, and tries to parse a date from
 // the line immediately after. Falls back to file mod time.
-func parseFrontMatter(raw []byte, slug, path string) (title string, body []byte, date time.Time) {
+// Also extracts optional og-image: and og-description: lines.
+func parseFrontMatter(raw []byte, slug, path string) (title string, body []byte, date time.Time, ogImage string, ogImageCustom bool, description string) {
 	body = raw
 
 	// Extract title
@@ -156,7 +177,27 @@ func parseFrontMatter(raw []byte, slug, path string) (title string, body []byte,
 		}
 	}
 
-	return title, body, date
+	// Strip og-image: and og-description: lines from body (can appear anywhere)
+	ogImageRe := regexp.MustCompile(`(?m)^og-image:\s*(.+)$`)
+	ogDescRe := regexp.MustCompile(`(?m)^og-description:\s*(.+)$`)
+
+	if m := ogImageRe.FindSubmatch(body); len(m) >= 2 {
+		ogImage = strings.TrimSpace(string(m[1]))
+		ogImageCustom = true
+		body = ogImageRe.ReplaceAll(body, nil)
+	}
+
+	if m := ogDescRe.FindSubmatch(body); len(m) >= 2 {
+		description = strings.TrimSpace(string(m[1]))
+		body = ogDescRe.ReplaceAll(body, nil)
+	}
+
+	// Auto-extract description from first paragraph if not set
+	if description == "" {
+		description = extractDescription(body)
+	}
+
+	return title, body, date, ogImage, ogImageCustom, description
 }
 
 func fileModTime(path string) time.Time {
@@ -166,3 +207,24 @@ func fileModTime(path string) time.Time {
 	}
 	return info.ModTime()
 }
+
+func extractDescription(body []byte) string {
+	// Find first non-empty line that isn't a markdown heading or front matter
+	lines := strings.Split(string(body), "\n")
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" || strings.HasPrefix(line, "#") || strings.HasPrefix(line, "---") {
+			continue
+		}
+		// Strip basic markdown formatting
+		desc := strings.ReplaceAll(line, "**", "")
+		desc = strings.ReplaceAll(desc, "*", "")
+		desc = strings.ReplaceAll(desc, "_", "")
+		// Truncate
+		if len(desc) > 160 {
+			desc = desc[:157] + "..."
+		}
+		return desc
+	}
+	return ""
+}