Remove unsafe-inline from the Content-Security-Policy (closes #125)

script-src and style-src now allow only 'self'. The generator page's
two inline onclick handlers, which selected the generated URL and
copied it, move into internal/static/generator.js and are attached
with addEventListener. The bundled Tailwind script, which built styles
in the browser and injected them at runtime, is replaced by a small
hand-written internal/static/style.css holding only the rules the
login and generator pages use; the templates carry a few plain class
names in place of Tailwind's. No build step. The pages keep their
layout, not every pixel of it.

Model: opus-5-5

internal/middleware/middleware.go

@@ -35,13 +35,10 @@ const HSTSValue = "max-age=31536000; includeSubDomains"
 
 // ContentSecurityPolicyValue is the Content-Security-Policy header value.
 // default-src 'self' is the baseline and frame-ancestors 'none' is the primary
-// clickjacking control. 'unsafe-inline' is required in script-src and style-src
-// because the served templates carry inline onclick handlers (generator page)
-// and the bundled Tailwind asset injects a runtime <style> element; dropping it
-// needs template changes outside this issue's scope.
+// clickjacking control.
 const ContentSecurityPolicyValue = "default-src 'self'; " +
-	"script-src 'self' 'unsafe-inline'; " +
-	"style-src 'self' 'unsafe-inline'; " +
+	"script-src 'self'; " +
+	"style-src 'self'; " +
 	"object-src 'none'; " +
 	"base-uri 'self'; " +
 	"form-action 'self'; " +

internal/middleware/middleware_internal_test.go

@@ -325,6 +325,13 @@ func TestSecurityHeaders_PolicyHeaders(t *testing.T) {
 
 	handler.ServeHTTP(rec, req)
 
+	// The login and generator pages load their script and stylesheet from
+	// /static, so the policy allows no inline script or style.
+	csp := rec.Header().Get("Content-Security-Policy")
+	if strings.Contains(csp, "unsafe-inline") {
+		t.Errorf("Content-Security-Policy allows unsafe-inline: %q", csp)
+	}
+
 	tests := []struct {
 		header string
 		want   string
@@ -333,8 +340,8 @@ func TestSecurityHeaders_PolicyHeaders(t *testing.T) {
 		{
 			"Content-Security-Policy",
 			"default-src 'self'; " +
-				"script-src 'self' 'unsafe-inline'; " +
-				"style-src 'self' 'unsafe-inline'; " +
+				"script-src 'self'; " +
+				"style-src 'self'; " +
 				"object-src 'none'; " +
 				"base-uri 'self'; " +
 				"form-action 'self'; " +