docs: move dns-automation plan to completed

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/plans/completed/dns-automation.md

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+# DNS Automation
+
+**Status:** Completed (2026-02-04)
+
+**Goal:** Automatically generate DNS entries from host configurations
+
+**Approach:** Leverage Nix to generate zone file entries from flake host configurations
+
+Since most hosts use static IPs defined in their NixOS configurations, we can extract this information and automatically generate A records. This keeps DNS in sync with the actual host configs.
+
+## Implementation
+
+- [x] Add optional CNAME field to host configurations
+  - [x] Added `homelab.dns.cnames` option in `modules/homelab/dns.nix`
+  - [x] Added `homelab.dns.enable` to allow opting out (defaults to true)
+  - [x] Documented in CLAUDE.md
+- [x] Create Nix function to extract DNS records from all hosts
+  - [x] Created `lib/dns-zone.nix` with extraction functions
+  - [x] Parses each host's `networking.hostName` and `systemd.network.networks` IP configuration
+  - [x] Collects CNAMEs from `homelab.dns.cnames`
+  - [x] Filters out VPN interfaces (wg*, tun*, tap*, vti*)
+  - [x] Generates complete zone file with A and CNAME records
+- [x] Integrate auto-generated records into zone files
+  - [x] External hosts separated to `services/ns/external-hosts.nix`
+  - [x] Zone includes comments showing which records are auto-generated vs external
+- [x] Update zone file serial number automatically
+  - [x] Uses `self.sourceInfo.lastModified` (git commit timestamp)
+- [x] Test zone file validity after generation
+  - [x] NSD validates zone at build time via `nsd-checkzone`
+- [x] Deploy process documented
+  - [x] Merge to master, run auto-upgrade on ns1/ns2
+
+## Files Created/Modified
+
+| File | Purpose |
+|------|---------|
+| `modules/homelab/dns.nix` | Defines `homelab.dns.*` options |
+| `modules/homelab/default.nix` | Module import hub |
+| `lib/dns-zone.nix` | Zone generation functions |
+| `services/ns/external-hosts.nix` | Non-flake host records |
+| `services/ns/master-authorative.nix` | Uses generated zone |
+| `services/ns/secondary-authorative.nix` | Uses generated zone |
+
+## Usage
+
+View generated zone:
+```bash
+nix eval .#nixosConfigurations.ns1.config.services.nsd.zones.'"home.2rjus.net"'.data --raw
+```
+
+Add CNAMEs to a host:
+```nix
+homelab.dns.cnames = [ "alias1" "alias2" ];
+```
+
+Exclude a host from DNS:
+```nix
+homelab.dns.enable = false;
+```
+
+Add non-flake hosts: Edit `services/ns/external-hosts.nix`