hosts: decommission ca host and remove labmon

Remove the step-ca host and labmon flake input now that ACME has been
migrated to OpenBao PKI.

Removed:
- hosts/ca/ - step-ca host configuration
- services/ca/ - step-ca service module
- labmon flake input and module (no longer used)

Updated:
- flake.nix - removed ca host and labmon references
- flake.lock - removed labmon input
- rebuild-all.sh - removed ca from host list
- CLAUDE.md - updated documentation

Note: secrets/ca/ should be manually removed by the user.

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

flake.lock

@@ -42,27 +42,6 @@
         "url": "https://git.t-juice.club/torjus/homelab-deploy"
       }
     },
-    "labmon": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs-unstable"
-        ]
-      },
-      "locked": {
-        "lastModified": 1748983975,
-        "narHash": "sha256-DA5mOqxwLMj/XLb4hvBU1WtE6cuVej7PjUr8N0EZsCE=",
-        "ref": "master",
-        "rev": "040a73e891a70ff06ec7ab31d7167914129dbf7d",
-        "revCount": 17,
-        "type": "git",
-        "url": "https://git.t-juice.club/torjus/labmon"
-      },
-      "original": {
-        "ref": "master",
-        "type": "git",
-        "url": "https://git.t-juice.club/torjus/labmon"
-      }
-    },
     "nixos-exporter": {
       "inputs": {
         "nixpkgs": [
@@ -119,7 +98,6 @@
       "inputs": {
         "alerttonotify": "alerttonotify",
         "homelab-deploy": "homelab-deploy",
-        "labmon": "labmon",
         "nixos-exporter": "nixos-exporter",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",