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/static/unlock.js

@@ -0,0 +1,7 @@
+// #139: unlock page: password reveal toggle.
+document.getElementById('pwreveal').addEventListener('click', () => {
+  const pw = document.getElementById('password');
+  const show = pw.type === 'password';
+  pw.type = show ? 'text' : 'password';
+  document.getElementById('pwreveal').title = show ? 'Hide password' : 'Show password';
+});