supernav: add cA2A to the cross-project switcher (#9)

cA2A (ca2a.agentrust-io.com) was missing from the shared top navigation,
so readers could not switch to it or see it highlighted as the active
site. Adds the SITES entry and the active-page detection branch.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: imran-siddique

supernav.js

@@ -7,6 +7,7 @@
     { id: 'trace',    label: 'TRACE',          url: 'https://trace.agentrust-io.com',                             dot: '#1B5EA0', ext: false },
     { id: 'manifest', label: 'Manifest',       url: 'https://manifest.agentrust-io.com',                          dot: '#1B7A4A', ext: false },
     { id: 'cmcp',       label: 'cMCP',        url: 'https://cmcp.agentrust-io.com',                            dot: '#6D28D9', ext: false },
+    { id: 'ca2a',       label: 'cA2A',           url: 'https://ca2a.agentrust-io.com',                            dot: '#0D9488', ext: false },
     { id: 'governance', label: 'Governance',  url: 'https://governance.agentrust-io.com',                       dot: '#EA580C', ext: false },
     { id: 'agt',        label: 'AGT',         url: 'https://github.com/microsoft/agent-governance-toolkit',    dot: '#6B7F94', ext: true  },
     { id: 'github',   label: 'GitHub',         url: 'https://github.com/agentrust-io',                           dot: '#8B949E', ext: true  }
@@ -17,6 +18,7 @@
     : HOST.indexOf('trace.') === 0    ? 'trace'
     : HOST.indexOf('manifest.') === 0 ? 'manifest'
     : HOST.indexOf('cmcp.') === 0        ? 'cmcp'
+    : HOST.indexOf('ca2a.') === 0        ? 'ca2a'
     : HOST.indexOf('governance.') === 0  ? 'governance'
     : HOST.indexOf('tests.') === 0       ? 'trace'
     : 'home';