feat(server): add owner-tools injection and inline code theme CSS

- Add owner-tools serving and injection for blog owners
- Inline code theme CSS in templates for soft reload support
- Update import paths from github.com/writekitapp to writekit
- Add optional session middleware for owner detection
- Update platform index with improved UI

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/server/platform.go

@@ -11,7 +11,7 @@ import (
 	"regexp"
 	"strings"
 
-	"github.com/writekitapp/writekit/internal/auth"
+	"writekit/internal/auth"
 )
 
 //go:embed templates/*.html