feat: add Loki log query support to lab-monitoring

Add 3 opt-in Loki tools (query_logs, list_labels, list_label_values)
that are registered when LOKI_URL is configured. Includes Loki HTTP
client, CLI commands (logs, labels), NixOS module option, formatting,
and tests.

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

README.md

@@ -18,13 +18,14 @@ Search and query Home Manager configuration options across multiple home-manager
 
 ### Lab Monitoring (`lab-monitoring`)
 
-Query Prometheus metrics and Alertmanager alerts from your monitoring stack. Unlike other servers, this queries live HTTP APIs — no database or indexing needed.
+Query Prometheus metrics, Alertmanager alerts, and Loki logs from your monitoring stack. Unlike other servers, this queries live HTTP APIs — no database or indexing needed.
 
 - List and inspect alerts from Alertmanager
 - Execute PromQL queries against Prometheus
 - Search metric names with metadata
 - View scrape target health
 - Manage alert silences
+- Query logs via LogQL (when Loki is configured)
 
 ### NixOS Options (`nixos-options`) - Legacy
 
@@ -97,7 +98,8 @@ Configure in your MCP client (e.g., Claude Desktop):
       "args": ["serve"],
       "env": {
         "PROMETHEUS_URL": "http://prometheus.example.com:9090",
-        "ALERTMANAGER_URL": "http://alertmanager.example.com:9093"
+        "ALERTMANAGER_URL": "http://alertmanager.example.com:9093",
+        "LOKI_URL": "http://loki.example.com:3100"
       }
     }
   }
@@ -135,7 +137,8 @@ Alternatively, if you have Nix installed, you can use the flake directly without
       "args": ["run", "git+https://git.t-juice.club/torjus/labmcp#lab-monitoring", "--", "serve"],
       "env": {
         "PROMETHEUS_URL": "http://prometheus.example.com:9090",
-        "ALERTMANAGER_URL": "http://alertmanager.example.com:9093"
+        "ALERTMANAGER_URL": "http://alertmanager.example.com:9093",
+        "LOKI_URL": "http://loki.example.com:3100"
       }
     }
   }
@@ -256,6 +259,15 @@ lab-monitoring targets
 # Search metrics
 lab-monitoring metrics node
 lab-monitoring metrics -n 20 cpu
+
+# Query logs from Loki (requires LOKI_URL)
+lab-monitoring logs '{job="varlogs"}'
+lab-monitoring logs '{job="nginx"} |= "error"' --start 2h --limit 50
+lab-monitoring logs '{job="systemd"}' --direction forward
+
+# List Loki labels
+lab-monitoring labels
+lab-monitoring labels --values job
 ```
 
 **Delete an indexed revision:**
@@ -276,6 +288,7 @@ hm-options delete release-23.11
 | `NIXOS_OPTIONS_DATABASE` | Database connection string for nixos-options (legacy) | `sqlite://nixos-options.db` |
 | `PROMETHEUS_URL` | Prometheus base URL for lab-monitoring | `http://localhost:9090` |
 | `ALERTMANAGER_URL` | Alertmanager base URL for lab-monitoring | `http://localhost:9093` |
+| `LOKI_URL` | Loki base URL for lab-monitoring (optional, enables log tools) | *(none)* |
 
 ### Database Connection Strings
 
@@ -336,6 +349,9 @@ hm-options -d "sqlite://my.db" index hm-unstable
 | `list_targets` | List scrape targets with health status |
 | `list_silences` | List active/pending alert silences |
 | `create_silence` | Create a new alert silence (requires `--enable-silences` flag) |
+| `query_logs` | Execute a LogQL range query against Loki (requires `LOKI_URL`) |
+| `list_labels` | List available label names from Loki (requires `LOKI_URL`) |
+| `list_label_values` | List values for a specific label from Loki (requires `LOKI_URL`) |
 
 ## NixOS Modules
 
@@ -489,6 +505,7 @@ Both `options.http` and `packages.http` also support:
 | `package` | package | from flake | Package to use |
 | `prometheusUrl` | string | `"http://localhost:9090"` | Prometheus base URL |
 | `alertmanagerUrl` | string | `"http://localhost:9093"` | Alertmanager base URL |
+| `lokiUrl` | nullOr string | `null` | Loki base URL (enables log query tools when set) |
 | `enableSilences` | bool | `false` | Enable the create_silence tool (write operation) |
 | `http.address` | string | `"127.0.0.1:8084"` | HTTP listen address |
 | `http.endpoint` | string | `"/mcp"` | HTTP endpoint path |