P4: Miniflux migration + PostgreSQL consolidation (#33)

## Summary
- Deploy miniflux in k8s via ArgoCD
- Expose via Tailscale Ingress at feed.tail8d86e.ts.net
- Retire brew PostgreSQL (no longer needed)
- Rename k8s-pg to pg (canonical hostname)
- Remove ansible miniflux and postgresql roles
- Update borgmatic to backup pg.tail8d86e.ts.net
- Update all zk documentation

## Deployment and Testing
- [x] Miniflux pod running in k8s
- [x] User login works at https://feed.tail8d86e.ts.net
- [x] Feeds and entries visible
- [x] brew miniflux and postgresql stopped
- [x] Tailscale services migrated (feed, pg)
- [x] zk documentation updated
- [x] Run ansible to apply role removals
- [ ] Verify borgmatic backup with new pg hostname

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: https://forge.tail8d86e.ts.net/eblume/blumeops/pulls/33

ansible/roles/borgmatic/tasks/main.yml

@@ -8,6 +8,17 @@
     state: directory
     mode: '0700'
 
+# .pgpass is used by pg_dump for database backups
+# Password is fetched in playbook pre_tasks as borgmatic_db_password
+- name: Write .pgpass file for borgmatic PostgreSQL backups
+  ansible.builtin.copy:
+    content: |
+      # Managed by ansible (borgmatic role) - k8s PostgreSQL backup credentials
+      pg.tail8d86e.ts.net:5432:*:borgmatic:{{ borgmatic_db_password }}
+    dest: ~/.pgpass
+    mode: '0600'
+  no_log: true
+
 - name: Deploy borgmatic configuration
   ansible.builtin.template:
     src: config.yaml.j2