Update docs to reflect community fork and recent changes

- Rewrite README: update all refs from shenxn to dancwilliams, remove deb
  build references, document what changed from upstream, simplify tags
  section, update all docker run and compose commands, add architecture
  table, add version update automation section, add credits
- Update SECURITY.md: replace shenxn contact with dancwilliams GitHub
  issue reporting, clarify scope (container vs bridge itself)
- Update docker-compose.yml: point to dancwilliams/protonmail-bridge,
  remove deprecated version key

SECURITY.md

@@ -1,5 +1,15 @@
 # Security Policy
 
+## Scope
+
+This policy covers security issues in the Docker container and associated scripts in this repository. It does not cover vulnerabilities in the Proton Bridge application itself — those should be reported directly to [Proton](https://proton.me/security).
+
 ## Reporting a Vulnerability
 
-Before reporting any vulnerability, make sure that it is caused by this project (i.e., this is not a vulnarability of the bridge itself). To report a vulnerabilitiy, you can send me an email (s@sxn.dev). My PGP public key is available [here](https://api.protonmail.ch/pks/lookup?op=get&search=s@sxn.dev).
+To report a security vulnerability in this project, please [open a GitHub issue](https://github.com/dancwilliams/protonmail-bridge-docker/issues) with the label `security`. For sensitive disclosures, you may also reach out via GitHub's private vulnerability reporting feature under the Security tab of this repository.
+
+Please include:
+- A description of the vulnerability
+- Steps to reproduce
+- Potential impact
+- Any suggested mitigations if known