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>

packages/server/package.json

@@ -15,6 +15,7 @@
   },
   "dependencies": {
     "@aws-sdk/client-s3": "^3.0.0",
+    "better-auth": "^1.5.5",
     "@hono/node-server": "^1.13.0",
     "bullmq": "^5.0.0",
     "dotenv": "^16.0.0",