Add comprehensive blog demo showcasing advanced content management features

- Implement complete mushroom foraging blog with chanterelles article
- Add rich demonstration of .insertr and .insertr-add functionality
- Include comprehensive documentation for future .insertr-content vision
- Update project styling and configuration to support blog demo
- Enhance engine and API handlers for improved content management

internal/engine/file.go

@@ -9,7 +9,6 @@ import (
 	"golang.org/x/net/html"
 )
 
-// ProcessFile processes a single HTML file (following Go stdlib pattern like os.ReadFile/WriteFile)
 func (e *ContentEngine) ProcessFile(inputPath, outputPath, siteID string, mode ProcessMode) error {
 	htmlContent, err := os.ReadFile(inputPath)
 	if err != nil {