Fix Docker signup, refresh docs, and improve blank invoice flow.

Parse DISABLE_SIGNUPS and related env booleans correctly for Compose string values, and derive auth trustedOrigins from BETTER_AUTH_URL. Rewrite README and architecture docs with the git.soconnor.dev remote and accurate deployment guidance. Allow zero-line-item draft invoices with validation when sending email.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/auth.ts

@@ -31,7 +31,8 @@ export const auth = betterAuth({
     },
   }),
   trustedOrigins: [
-    "https://beenvoice.soconnor.dev",
+    ...(process.env.BETTER_AUTH_URL ? [process.env.BETTER_AUTH_URL] : []),
+    ...(process.env.NEXT_PUBLIC_APP_URL ? [process.env.NEXT_PUBLIC_APP_URL] : []),
     "beenvoice://",
     "exp://",
     ...(authentikOrigin ? [authentikOrigin] : []),