add woodpecker-peek input + cache to attic via CI

Re-exposes oleks/woodpecker-peek as packages.<sys>.woodpecker-peek for
x86_64-linux and aarch64-linux, and adds it to ci/build.py so the
amd64/arm64 workflows push the closure to attic-infra-cache-k3s-1.
Consumers (emmett) then set services.woodpecker-peek.package = pkgs.woodpecker-peek
and pull the cached binary instead of rebuilding.

flake.lock

@@ -191,7 +191,8 @@
           "fleet-pins",
           "nixpkgs-projects"
         ],
-        "stalewood": "stalewood"
+        "stalewood": "stalewood",
+        "woodpecker-peek": "woodpecker-peek"
       }
     },
     "stalewood": {
@@ -258,6 +259,27 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "woodpecker-peek": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1779635650,
+        "narHash": "sha256-teMrDHA/Q/KZugO8lSG96+r9+L9rNjb2MDXprFhL6Hc=",
+        "ref": "main",
+        "rev": "804f2bf8c8990ce4e13548a4b3a917661f32d8bc",
+        "revCount": 3,
+        "type": "git",
+        "url": "https://git.oleks.space/oleks/woodpecker-peek"
+      },
+      "original": {
+        "ref": "main",
+        "type": "git",
+        "url": "https://git.oleks.space/oleks/woodpecker-peek"
+      }
     }
   },
   "root": "root",