feat: Simplify AutoStart and fix critical security vulnerability

Major architectural improvements:
- Remove complex plaintext cache system, use direct database fields
- Replace IP-based authentication with secure token-based auth
- Integrate INTERNAL_AUTH_TOKEN with unified auto-generation system

Security fixes:
- Fix Docker nginx proxy authentication bypass vulnerability in /ssh/db/host/internal
- Replace req.ip detection with X-Internal-Auth-Token header validation
- Add production environment security checks for internal auth token

AutoStart simplification:
- Add autostart_{password,key,key_password} columns directly to ssh_data table
- Remove redundant autostartPlaintextCache table and AutoStartPlaintextManager
- Implement enable/disable/status endpoints for autostart management
- Update frontend to handle autostart cache lifecycle automatically

Environment variable improvements:
- Integrate INTERNAL_AUTH_TOKEN into SystemCrypto auto-generation
- Unified .env file management for all security keys (JWT, Database, Internal Auth)
- Auto-generate secure tokens with proper entropy (256-bit)

API improvements:
- Make /users/oidc-config and /users/registration-allowed public for login page
- Add /users/setup-required endpoint replacing problematic getUserCount usage
- Restrict /users/count to admin-only access for security

Database schema:
- Add autostart plaintext columns to ssh_data table with proper migrations
- Remove complex cache table structure for simplified data model

src/ui/Desktop/Homepage/HomepageAuth.tsx

@@ -13,7 +13,7 @@ import {
   getUserInfo,
   getRegistrationAllowed,
   getOIDCConfig,
-  getUserCount,
+  getSetupRequired,
   initiatePasswordReset,
   verifyPasswordResetCode,
   completePasswordReset,
@@ -124,9 +124,9 @@ export function HomepageAuth({
   }, []);
 
   useEffect(() => {
-    getUserCount()
+    getSetupRequired()
       .then((res) => {
-        if (res.count === 0) {
+        if (res.setup_required) {
           setFirstUser(true);
           setTab("signup");
         } else {