Fix #139: drop unsafe-inline from script-src and style-src (#139)

- Move all inline <script> blocks (layout head/theme, topbar dark toggle,
  foot, paste, new, history, mine, settings, admin, unlock) to external
  files under internal/web/static/. Page data reaches scripts via data-*
  attributes (data-paste-id, data-default-dark) instead of template vars.
- Replace inline onclick handlers (copy, delete, stats toggle) with
  addEventListener wiring.
- Convert inline style="" attributes to CSS utility classes; swatch
  colors are now set via CSSOM/DOM APIs instead of innerHTML strings.
- script-src/style-src are now plain 'self'; img-src data: stays for the
  SVG data-URI backgrounds. Verified with headless chromium: zero CSP
  violations on all pages in dark and light presets, theme swatches,
  admin lock, tables and paste view render correctly.

internal/web/csp_noinline_test.go

@@ -0,0 +1,56 @@
+package web
+
+import (
+	"embed"
+	"io/fs"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// #139 regression guards: with CSP script-src/style-src 'self' (no
+// 'unsafe-inline'), the templates must not carry inline <script> blocks or
+// style="" attributes, and the external scripts referenced must exist.
+func TestNoInlineScripts(t *testing.T) {
+	entries, err := fs.ReadDir(tmplFS, "templates")
+	if err != nil {
+		t.Fatal(err)
+	}
+	re := regexp.MustCompile(`(?s)<script[^>]*>.*?</script>`)
+	srcOnly := regexp.MustCompile(`<script[^>]+src=`)
+	for _, e := range entries {
+		b, err := fs.ReadFile(tmplFS, "templates/"+e.Name())
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, m := range re.FindAll(b, -1) {
+			if srcOnly.Match(m) {
+				continue // external script tag with src: fine
+			}
+			t.Errorf("%s: inline <script> block found (CSP #139): %q", e.Name(), string(m[:60]))
+		}
+		if strings.Contains(string(b), " onclick=") || strings.Contains(string(b), "onload=") {
+			t.Errorf("%s: inline event handler attribute found (CSP #139)", e.Name())
+		}
+		if strings.Contains(string(b), "style=\"") {
+			t.Errorf("%s: inline style attribute found (CSP #139)", e.Name())
+		}
+	}
+}
+
+func TestReferencedStaticScriptsExist(t *testing.T) {
+	entries, _ := fs.ReadDir(tmplFS, "templates")
+	var staticFiles embed.FS = staticFS
+	for _, e := range entries {
+		b, err := fs.ReadFile(tmplFS, "templates/"+e.Name())
+		if err != nil {
+			t.Fatal(err)
+		}
+		for _, m := range regexp.MustCompile(`<script src="/static/([^"]+)"`).FindAllSubmatch(b, -1) {
+			name := string(m[1])
+			if _, err := fs.ReadFile(staticFiles, "static/"+name); err != nil {
+				t.Errorf("%s references /static/%s: %v", e.Name(), name, err)
+			}
+		}
+	}
+}