Complete Better Auth migration, harden security, update all docs

Console:
- Rewrite auth from JWT decoding to Better Auth useSession()
- Add auth-client.ts with createAuthClient
- Remove elydora_token localStorage, dead auth API functions
- Fix login/register pages to use signIn.email/signUp.email

Server:
- Upgrade better-auth ^1.2.0 → ^1.5.5
- CORS: enforce allowlist on all environments
- Sync auth service and middleware with backend

SDKs:
- Deprecate login/register in Node, Python, Go SDKs
- Update READMEs to show direct token initialization

Config:
- Sanitize .env with dev-only placeholder values
- Update helm chart and install scripts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sdks/node/src/client.ts

@@ -65,7 +65,7 @@ export class ElydoraClient {
   }
 
   /**
-   * Set the JWT token used for authenticated API calls.
+   * Set the session token used for authenticated API calls.
    */
   setToken(token: string): void {
     this.token = token;
@@ -89,6 +89,9 @@ export class ElydoraClient {
   // Auth (static methods — no instance needed)
   // -------------------------------------------------------------------------
 
+  /**
+   * @deprecated Use Better Auth endpoints directly. See docs.
+   */
   static async register(
     baseUrl: string,
     email: string,
@@ -110,6 +113,9 @@ export class ElydoraClient {
     return handleResponse<AuthRegisterResponse>(res);
   }
 
+  /**
+   * @deprecated Use Better Auth endpoints directly. See docs.
+   */
   static async login(
     baseUrl: string,
     email: string,