Switch firstmate to OpenCode 2 and refresh nix-darwin pins

Point fm at the isolated oc2 wrapper, upgrade Homebrew packages on rebuild, and declare ffmpeg, docker-desktop, puremac, utm, node, and tea. Update nixpkgs, home-manager, and nix-homebrew locks. Track Pi agent config, crew-dispatch, and the Gitea PR helper that home.nix already expected.

home/.config/firstmate/crew-dispatch.json

@@ -0,0 +1,20 @@
+{
+  "rules": [
+    {
+      "when": "pure-function implementation with tests (indicators, slots, seasonal wiring, repositories)",
+      "use": [{ "harness": "pi", "model": "opencode-go/mimo-v2.5-pro" }],
+      "why": "MiMo V2.5 Pro (opencode-go, 1M ctx) produces clean correct code; flat-rate sub so $0 marginal cost. Pi drives it in an isolated worktree."
+    },
+    {
+      "when": "adapter or external-fetch integration (COT, seed backfills, vendor seams)",
+      "use": [{ "harness": "pi", "model": "opencode-go/mimo-v2.5-pro" }],
+      "why": "Pattern-following work against existing adapter contracts; MiMo handles iterative fetch/debug loops."
+    },
+    {
+      "when": "frontend page or tRPC wiring (UI panels, router procedures, client exposure)",
+      "use": [{ "harness": "pi", "model": "opencode-go/mimo-v2.5-pro" }],
+      "why": "Mechanical wiring against existing components/routers; the contract carries the specialization."
+    }
+  ],
+  "default": [{ "harness": "pi", "model": "opencode-go/mimo-v2.5-pro" }]
+}