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.

SECURITY.md

@@ -4,18 +4,19 @@
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 0.2.x   | Yes                |
+| 0.2.x+  | Yes                |
 | < 0.2   | No                 |
 
 ## Reporting a Vulnerability
 
 **Please do not open a public issue for security vulnerabilities.**
 
-Instead, use GitHub's private vulnerability reporting:
+You can report security issues in two ways:
 
-1. Go to the [Security tab](https://github.com/AnsoCode/Sencho/security) of this repository
-2. Click **"Report a vulnerability"**
-3. Provide details including: steps to reproduce, impact assessment, and any suggested fixes
+1. **Email:** Send details to **security@sencho.io**
+2. **GitHub:** Use [private vulnerability reporting](https://github.com/AnsoCode/Sencho/security/advisories/new) in the Security tab
+
+In your report, include: steps to reproduce, impact assessment, and any suggested fixes.
 
 You can expect an initial response within 72 hours. We will work with you to understand and address the issue before any public disclosure.