chore: prepare repo for public release — scrub internal infra, rewrite README

- Remove owner-specific / legacy deploy files (home/prod/server compose, deploy/).
  The home compose stays as a local untracked file for the maintainer's own deploy.
- Genericise infra-specific code comments (egress-proxy examples) to neutral wording.
- Replace the hardcoded contact email on the legal pages with the instance operator's
  configured admin email, served via the public /auth/config and shown with a neutral
  fallback — so each self-hosted instance shows its own contact.
- Rewrite README for the current app + a copy-paste self-hosting quick start (prebuilt
  image + first-run wizard) with a build-from-source alternative; tidy .env.example.

frontend/src/lib/api.ts

@@ -773,8 +773,11 @@ export const api = {
     }),
 
   // Public: which sign-in options this instance offers (e.g. hide Google when not configured).
-  authConfig: (): Promise<{ google_enabled: boolean; allow_registration: boolean }> =>
-    req("/auth/config"),
+  authConfig: (): Promise<{
+    google_enabled: boolean;
+    allow_registration: boolean;
+    operator_contact: string | null;
+  }> => req("/auth/config"),
 
   // --- first-run install wizard (token from the setup URL printed to the container logs) ---
   setupStatus: (): Promise<{ configured: boolean }> => req("/api/setup/status"),