feat(dev): add gastown multi-agent workspace manager

- Add gastown flake input (non-flake, source only)
- Build gastown package using buildGoModule in development role
- Configure renovate for daily updates of gastown and beads
- Binary: gt (Gas Town CLI by Steve Yegge)

flake.lock

@@ -78,6 +78,22 @@
         "type": "github"
       }
     },
+    "gastown": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1768682809,
+        "narHash": "sha256-PCP5PQasLqL5/OVNw6LsjiFfIU4RNniicTUcVq2ggHg=",
+        "owner": "steveyegge",
+        "repo": "gastown",
+        "rev": "9cd2696abe68ac0defc612ace5028d327d4f207d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "steveyegge",
+        "repo": "gastown",
+        "type": "github"
+      }
+    },
     "google-cookie-retrieval": {
       "inputs": {
         "nixpkgs": [
@@ -306,6 +322,7 @@
     "root": {
       "inputs": {
         "beads": "beads",
+        "gastown": "gastown",
         "google-cookie-retrieval": "google-cookie-retrieval",
         "home-manager": "home-manager",
         "home-manager-unstable": "home-manager-unstable",