Coder: déploiement Helm via ArgoCD (apps/coder/)

## Contexte
Déploiement du chart Helm officiel `coder/coder` (https://helm.coder.com), sur le modèle multi-source ArgoCD de `apps/planka/planka.argoapp.yaml`.

## À faire
- [ ] `apps/coder/coder.argoapp.yaml` : `Application` multi-source (chart `coder/coder` + `values.yaml` versionné + overlay `resources/`)
- [ ] `apps/coder/helm/values.yaml` : `CODER_PG_CONNECTION_URL` (secret CNPG de l'issue https://github.com/ClubCedille/k8s-shared/issues/319), `CODER_OIDC_*` (secret Vault de l'issue https://github.com/ClubCedille/k8s-shared/issues/318), wildcard access URL
- [ ] `apps/coder/resources/certificate.yaml` + `httpproxy.yaml` (incluant la route wildcard `*.coder.etsmtl.club`)

## Dépend de
https://github.com/ClubCedille/k8s-shared/issues/317, https://github.com/ClubCedille/k8s-shared/issues/318, https://github.com/ClubCedille/k8s-shared/issues/319

Start by reading apps/planka/planka.argoapp.yaml as the stated multi-source ArgoCD model, then inspect the requested apps/coder/ files. Check issues 317, 318, and 319 before wiring the PostgreSQL and Vault secrets. Done means the Application, values, certificate, and HTTPProxy resources are present with the wildcard Coder route and referenced settings.

Written by the indexing model from the issue text.