feat(contact): add official contact emails throughout app and docs (#428)

Surface six dedicated email channels (support, contact, licensing,
security, privacy, conduct) across contextually appropriate locations:

- security.txt: create .well-known/security.txt for app (RFC 9116)
- SECURITY.md: add security@sencho.io as alternative to GitHub reporting
- PaidGate/AdmiralGate: add licensing@sencho.io to upgrade prompts
- docs: new Contact & Support reference page listing all channels
- CHANGELOG: document additions under [Unreleased]

Website changes (separate repo): privacy@sencho.io in Privacy/Terms
pages, licensing@sencho.io in Refund page and pricing footer,
contact@sencho.io in website footer.

frontend/src/components/AdmiralGate.tsx

@@ -47,6 +47,8 @@ export function AdmiralGate({ children, featureName = 'This feature' }: AdmiralG
                 <h3 className="text-lg font-semibold mb-2">{featureName} requires Sencho Admiral</h3>
                 <p className="text-sm text-muted-foreground">
                     Unlock team features like SSO authentication, audit logging, API tokens, and unlimited user accounts with a Sencho Admiral license.
+                    For enterprise pricing or questions, contact{' '}
+                    <a href="mailto:licensing@sencho.io" className="text-brand hover:underline">licensing@sencho.io</a>.
                 </p>
             </div>
             <div className="flex gap-3">

frontend/src/components/PaidGate.tsx

@@ -47,6 +47,8 @@ export function PaidGate({ children, featureName = 'This feature' }: PaidGatePro
                 <h3 className="text-lg font-semibold mb-2">{featureName} requires a paid license</h3>
                 <p className="text-sm text-muted-foreground">
                     Unlock features like fleet management, viewer accounts, and more with a Skipper or Admiral license.
+                    For enterprise pricing or questions, contact{' '}
+                    <a href="mailto:licensing@sencho.io" className="text-brand hover:underline">licensing@sencho.io</a>.
                 </p>
             </div>
             <div className="flex gap-3">