grafana: replace custom metric collectors with community exporters

Replace three custom Prometheus textfile collector scripts with
dedicated community-maintained exporters:

- jellyfin-collector.nix (25 LoC shell) -> rebelcore/jellyfin_exporter
  Metric: jellyfin_active_streams -> count(jellyfin_now_playing_state)
  Bonus: per-session labels (user, title, device, codec info)

- qbittorrent-collector.nix (40 LoC shell) -> anriha/qbittorrent-metrics-exporter
  Metric: qbittorrent_{download,upload}_bytes_per_second -> qbit_{dl,up}speed
  Bonus: per-torrent metrics with category/tag aggregation

- intel-gpu-collector.nix + .py (130 LoC Python) -> mike1808/igpu-exporter
  Metric: intel_gpu_engine_busy_percent -> igpu_engines_busy_percent
  Bonus: persistent daemon vs oneshot timer, no streaming JSON parser

All three run as persistent daemons scraped by Prometheus, replacing
the textfile-collector pattern of systemd timers writing .prom files.
Dashboard PromQL queries updated to match new metric names.

flake.lock

@@ -102,6 +102,29 @@
         "type": "github"
       }
     },
+    "fenix": {
+      "inputs": {
+        "nixpkgs": [
+          "qbittorrent-metrics-exporter",
+          "naersk",
+          "nixpkgs"
+        ],
+        "rust-analyzer-src": "rust-analyzer-src"
+      },
+      "locked": {
+        "lastModified": 1752475459,
+        "narHash": "sha256-z6QEu4ZFuHiqdOPbYss4/Q8B0BFhacR8ts6jO/F/aOU=",
+        "owner": "nix-community",
+        "repo": "fenix",
+        "rev": "bf0d6f70f4c9a9cf8845f992105652173f4b617f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "fenix",
+        "type": "github"
+      }
+    },
     "flake-compat": {
       "flake": false,
       "locked": {
@@ -170,7 +193,7 @@
     },
     "flake-utils": {
       "inputs": {
-        "systems": "systems_4"
+        "systems": "systems_5"
       },
       "locked": {
         "lastModified": 1731533236,
@@ -316,6 +339,26 @@
         "type": "github"
       }
     },
+    "naersk": {
+      "inputs": {
+        "fenix": "fenix",
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1763384566,
+        "narHash": "sha256-r+wgI+WvNaSdxQmqaM58lVNvJYJ16zoq+tKN20cLst4=",
+        "owner": "nix-community",
+        "repo": "naersk",
+        "rev": "d4155d6ebb70fbe2314959842f744aa7cabbbf6a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "ref": "master",
+        "repo": "naersk",
+        "type": "github"
+      }
+    },
     "nix-minecraft": {
       "inputs": {
         "flake-compat": "flake-compat_3",
@@ -400,6 +443,22 @@
       }
     },
     "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1752077645,
+        "narHash": "sha256-HM791ZQtXV93xtCY+ZxG1REzhQenSQO020cu6rHtAPk=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "be9e214982e20b8310878ac2baa063a961c1bdf6",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_3": {
       "locked": {
         "lastModified": 1764517877,
         "narHash": "sha256-pp3uT4hHijIC8JUK5MEqeAWmParJrgBVzHLNfJDZxg4=",
@@ -438,6 +497,28 @@
         "type": "github"
       }
     },
+    "qbittorrent-metrics-exporter": {
+      "inputs": {
+        "naersk": "naersk",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "systems": "systems_4"
+      },
+      "locked": {
+        "lastModified": 1771989937,
+        "narHash": "sha256-bPUV4gVvSbF4VMkbLKYrfwVwzTeS+Sr41wucDj1///g=",
+        "ref": "refs/heads/main",
+        "rev": "cb94f866b7a2738532b1cae31d0b9f89adecbd54",
+        "revCount": 112,
+        "type": "git",
+        "url": "https://codeberg.org/anriha/qbittorrent-metrics-exporter"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://codeberg.org/anriha/qbittorrent-metrics-exporter"
+      }
+    },
     "root": {
       "inputs": {
         "agenix": "agenix",
@@ -452,6 +533,7 @@
         "nixos-hardware": "nixos-hardware",
         "nixpkgs": "nixpkgs",
         "nixpkgs-p2pool-module": "nixpkgs-p2pool-module",
+        "qbittorrent-metrics-exporter": "qbittorrent-metrics-exporter",
         "senior_project-website": "senior_project-website",
         "srvos": "srvos",
         "trackerlist": "trackerlist",
@@ -460,6 +542,23 @@
         "ytbn-graphing-software": "ytbn-graphing-software"
       }
     },
+    "rust-analyzer-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1752428706,
+        "narHash": "sha256-EJcdxw3aXfP8Ex1Nm3s0awyH9egQvB2Gu+QEnJn2Sfg=",
+        "owner": "rust-lang",
+        "repo": "rust-analyzer",
+        "rev": "591e3b7624be97e4443ea7b5542c191311aa141d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "rust-lang",
+        "ref": "nightly",
+        "repo": "rust-analyzer",
+        "type": "github"
+      }
+    },
     "rust-overlay": {
       "inputs": {
         "nixpkgs": [
@@ -598,6 +697,21 @@
         "type": "github"
       }
     },
+    "systems_5": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
     "trackerlist": {
       "flake": false,
       "locked": {
@@ -666,7 +780,7 @@
     "ytbn-graphing-software": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs_2",
+        "nixpkgs": "nixpkgs_3",
         "rust-overlay": "rust-overlay_2"
       },
       "locked": {