Add monitoring profile: Grafana + Prometheus + Loki + Alloy

Native NixOS modules under my.profiles.monitoring, enabled on jupiter.
Grafana provisions datasources/dashboards/alert rules from the
grafana-content flake input (rechberg dashboards repo). Prometheus
scrapes host + stack (90d), Loki+Alloy ship the systemd journal (90d).
Grafana LAN-only :3000, anonymous viewer, admin password + secret_key
via /etc/grafana file providers.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CZJkwCnSbykq9rRTTeHc6b

flake.lock

@@ -79,6 +79,22 @@
         "type": "github"
       }
     },
+    "grafana-content": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1785940786,
+        "narHash": "sha256-flH5pwYtB3QWnZ/OYJKoj9twb1fxYrowr9FCh8L1GMY=",
+        "ref": "refs/heads/master",
+        "rev": "4017b678ffa3bde4136a3468f18f1eb3bba52374",
+        "revCount": 1,
+        "type": "git",
+        "url": "ssh://git@rechberg.online:222/finn.markwitz/dashboards.git"
+      },
+      "original": {
+        "type": "git",
+        "url": "ssh://git@rechberg.online:222/finn.markwitz/dashboards.git"
+      }
+    },
     "nix": {
       "inputs": {
         "flake-compat": "flake-compat",
@@ -260,6 +276,7 @@
     "root": {
       "inputs": {
         "flake-parts": "flake-parts",
+        "grafana-content": "grafana-content",
         "nix": "nix",
         "nixos-generators": "nixos-generators",
         "nixos-hardware": "nixos-hardware",