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/foot.js

@@ -0,0 +1,19 @@
+// #46: live relative-time counters: tick any [data-ts] (epoch seconds) every second
+(function () {
+  function fmt(ts) {
+    const s = Math.max(0, Math.floor(Date.now() / 1000) - ts);
+    if (s < 60) return s + 's ago';
+    if (s < 3600) return Math.floor(s / 60) + 'm ago';
+    if (s < 86400) return Math.floor(s / 3600) + 'h ago';
+    return Math.floor(s / 86400) + 'd ago';
+  }
+  function tick() {
+    document.querySelectorAll('[data-ts]').forEach(el => {
+      const ts = parseInt(el.dataset.ts, 10);
+      if (!isNaN(ts)) el.textContent = fmt(ts);
+    });
+  }
+  setInterval(tick, 1000);
+  document.addEventListener('DOMContentLoaded', tick);
+  tick();
+})();