Add Argo Project + namespaces for observability components

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Goal
Keep platform apps from polluting each other and enforce clean RBAC/sync boundaries.

Scope / Tasks

Create or update Argo Project:

argocd/projects/coachlight-k3s-observability-project.yml (name per your convention)

Namespaces:

observability

Update each Argo Application to target the project + namespace

Acceptance Criteria

Argo Project limits destinations and source repos appropriately

Apps deploy into correct namespaces with no cross-namespace accidental sprawl