feat(site): multi-site join server endpoints + persisted site role + emoji fix

Server endpoints for joining a spoke to a master directory (MULTI_SITE_SPEC.md).
This pass is server-only; setup.sh wiring and the UI are the next layer.

- Site join keys (SiteJoinKey model, stj_ prefix): mint/revoke/delete/list,
  hashed at rest, shown once — the same model as agent join keys.
- POST /api/site/export (master, Bearer stj_ key, no admin session): returns the
  local LDAP tree (slapcat LDIF) + resource catalog + siteSlug + baseDn.
- POST /api/site/join (spoke, admin): { masterUrl, joinKey } pulls the master
  export, imports resources (upsert by slug) + LDAP (ldapadd -c), and persists
  the spoke role. Refused if already a spoke.
- Persisted site role: utils/site_config.js keeps isMaster/masterUrl/siteSlug in
  /config/site.json (env seeds defaults); site-status/site-promote now use it.
- Unit tests (site_join, site_config) with in-memory stubs, wired into npm test.
- docs/site-join.md + docs router entry.
- Repairs the corrupted multi-site emojis (crown/bolt) in directory.ejs.
- .gitguardian.yml ignores the generic-password false positive on reading the
  LDAP bind credential from runtime config (never a hardcoded secret).

nodejs/routes/docs.js

@@ -42,6 +42,7 @@ const DOCS = {
 	discovery:       {title: 'Discovery & Inventory',  file: path.join(__dirname, '../../docs/discovery.md')},
 	vault:           {title: 'Vault Secrets',           file: path.join(__dirname, '../../docs/vault.md')},
 	groups:          {title: 'Groups & Permissions',   file: path.join(__dirname, '../../docs/groups.md')},
+	'site-join':     {title: 'Multi-Site: Joining a Spoke', file: path.join(__dirname, '../../docs/site-join.md')},
 
 	overview:        {title: 'Overview',        file: path.join(__dirname, '../../README.md')},
 	changelog:       {title: 'Changelog',       file: path.join(__dirname, '../../CHANGELOG.md')},