Add a footer, move GitHub link out of the nav (#130)

proxy had no page footer at all — no copyright, no license link, no
build/version info — unlike sso-manager-node, which already had one
(now cleaned up in a matching change there). Bring the two in line:

- Added a footer to bottom.ejs: theta42 logo/link, "© <year> theta42"
  with an MIT License link, a GitHub link, and build version/hash.
- Moved the GitHub icon link out of the top nav (where it competed
  with actual navigation items) and into the new footer.
- Added nodejs/utils/build_info.js (buildVersion/buildHash/buildYear,
  read once from package.json + git) and wired it into routes/render.js
  so every page has the values the footer needs. Mirrors the same
  helper added to sso-manager-node in the matching cleanup there.
- Copied the theta42.svg logo into nodejs/public/img/ (previously only
  present in sso-manager-node) so both apps' footers render identically.

Verified by rendering top+bottom with the real ejs package: no
template errors, GitHub link present exactly once (in the footer, not
the nav), logo and MIT License link present. npm test: 192/192 pass
(unaffected — view-only + a new leaf utility module).

nodejs/utils/build_info.js

@@ -0,0 +1,15 @@
+'use strict';
+
+const { execSync } = require('child_process');
+const { version: buildVersion } = require('../package.json');
+
+let buildHash = 'unknown';
+try {
+	buildHash = execSync('git rev-parse --short HEAD', { cwd: __dirname }).toString().trim();
+} catch (_) {}
+
+module.exports = {
+	buildVersion,
+	buildHash,
+	buildYear: new Date().getFullYear(),
+};