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>

.env.example

@@ -20,7 +20,8 @@ PORT=8787
 ENVIRONMENT=production
 API_VERSION=v1
 PROTOCOL_VERSION=1.0
-JWT_SECRET=GENERATE_ME
+BETTER_AUTH_SECRET=GENERATE_ME
+BETTER_AUTH_URL=http://localhost:8787
 ELYDORA_SIGNING_KEY=GENERATE_ME
 ALLOWED_ORIGINS=http://localhost:3000