Clean up footer: fix copyright, move GitHub link out of the nav (#41)

- Copyright was "© <year> <name>" where <name> is conf.name — an
  operator-configurable display name (e.g. whatever CFG_ORG is set
  to), not a real copyright holder. Changed to "© <year> theta42",
  matching the LICENSE file. Also dropped "All rights reserved",
  which contradicts the MIT license this project ships under; added
  an explicit MIT License link instead.
- Moved the GitHub icon link out of the top nav (where it competed
  with actual navigation items) and into the footer, alongside the
  license link and version/build info.
- Deduplicated the identical buildVersion/buildHash/buildYear
  computation that was copy-pasted in both routes/index.js and
  routes/oauth.js into a shared nodejs/utils/build_info.js.

Verified by rendering top+bottom with the real ejs package: no
template errors, GitHub link present exactly once (in the footer,
not the nav), "All rights reserved" gone, MIT License link present.
npm test failures (155) are pre-existing/environmental (no LDAP
server here) — identical failure count with these changes stashed
out.

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(),
+};