Initial infrastructure mono-repo scaffold

Consolidates nixos, docker, raspi, and debian-configuration into a single
infrastructure-as-code repo. Includes:

- ansible/: full inventory + proxmox-hardening, freeipa, and raspberrypi
  roles (converted from debian-configuration bash scripts)
- terraform/: Proxmox VMs, Dynu DNS, Pi-hole (decommissioned stub),
  Docker container catalog — migrated from docker/infrastructure/terraform/
- stacks/docker/, stacks/raspi/, nixos/: placeholder READMEs pending
  git subtree population (see implementation plan)
- docs/: internal MkDocs site with architecture, network topology, runbooks,
  and drift-detection guide; external sanitized site
- scripts/: drift-detect.sh, docs-build.sh, install-hooks.sh, check-secrets.sh
- CI: secret-scan (push/PR), drift-detect (daily), docs-build (on change)
- Pi-hole removed throughout — DNS is FreeIPA, DHCP is router

See docs/internal/implementation-plan.md for the phased rollout after
pushing to Gitea.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UvNjoxTWEDkhXsd1Dq2ETP

docs/internal/runbooks/drift-detection.md

@@ -0,0 +1,64 @@
+# Runbook: Drift Detection
+
+How to interpret and respond to drift detected by the CI pipeline or local script.
+
+## What is drift?
+
+**Terraform drift** — a Proxmox VM, DNS record, or Pi-hole entry exists in a different
+state than what's declared in the Terraform workspace. Common causes:
+- A VM was resized or reconfigured manually in the PVE web UI
+- A DNS record was added directly via Dynu or Pi-hole admin
+- A VM was deleted outside of Terraform
+
+**Ansible drift** — a host's configuration differs from what the Ansible role declares.
+Common causes:
+- A config file was edited by hand on the host
+- A package was installed/removed manually
+- A service was stopped/disabled without updating the role
+
+## CI workflow
+
+The `drift-detect` workflow runs daily at 06:00 AEST. If drift is detected, a Gotify
+notification is sent to the push notification dashboard. The step summary in Gitea CI
+contains the full `terraform plan` diff.
+
+## Responding to Terraform drift
+
+```bash
+# See exactly what changed
+cd terraform/proxmox
+terraform plan
+
+# Option A: The manual change was intentional — update the .tf file to match reality,
+# then run terraform apply to reconcile state
+vim proxmox/docker.tf  # update the resource to match current state
+terraform apply
+
+# Option B: The manual change was accidental — apply to restore declared state
+terraform apply  # will revert the manual change
+```
+
+## Responding to Ansible drift
+
+```bash
+# See exactly what would change
+cd ansible
+ansible-playbook playbooks/site.yml --check --diff --limit <drifted_host>
+
+# Apply to restore declared state
+ansible-playbook playbooks/site.yml --limit <drifted_host>
+```
+
+## Required Gitea secrets
+
+The following secrets must be configured in the Gitea repo for CI drift detection to work:
+
+| Secret | Used by |
+|--------|---------|
+| `PROXMOX_ENDPOINT` | Terraform proxmox workspace |
+| `PROXMOX_API_TOKEN_ID` | Terraform proxmox workspace |
+| `PROXMOX_API_TOKEN_SECRET` | Terraform proxmox workspace |
+| `DYNU_API_KEY` | Terraform dns workspace |
+| `ANSIBLE_SSH_KEY` | Ansible drift check |
+| `GOTIFY_URL` | Drift notifications |
+| `GOTIFY_TOKEN` | Drift notifications |