Update Helm chart for v0.2.0 Go release

[dhilgaertner]

Problem

The Helm chart still has Python-era artifacts from before the Go port, and several defaults don't match the Go app. This causes:

1. Chart won't deploy: command: ["uvicorn", ...] override and Python init container fail with the Go image
2. Silent CrashLoop: UI_SESSION_SECRET not exposed — production users get opaque CrashLoopBackOff
3. Default mismatches: passthrough.enabled and guardrails.openaiModeration defaults differ from Go app
4. Stale docs: Bitnami repo step, Python troubleshooting commands, wrong health response format

Changes

Critical Fixes

• Remove uvicorn command override and PYTHONPATH env var from deployment
• Replace Python/asyncpg init container with busybox + nc TCP check
• Bump version and appVersion to 0.2.0

New-User Friction Fixes

• Add citadel.uiSessionSecret value and wire it into secrets.yaml
• Change passthrough.enabled default to true (matches Go app)
• Change guardrails.openaiModeration default to true (matches Go app)
• Improve NOTES.txt with API key creation guidance and PVC cleanup reminder

Documentation

• Remove unnecessary "Add Bitnami repo" step
• Fix health response format ("ok" not "healthy")
• Replace Python troubleshooting command with curl health check
• Update image tag references from 0.1.0 to 0.2.0
• Add uiSessionSecret to production hardening checklist
• Add CHANGELOG.md entry for 0.2.0

Verification

Tested on Docker Desktop Kubernetes — clean install, health checks pass, UI accessible, Helm test succeeds.