config: subagents -> opencode/deepseek-v4-flash (zen endpoint, not tinfoil)

Route deepseek-v4-flash through the opencode zen subscription endpoint
(opencode/deepseek-v4-flash) instead of tinfoil pay-per-use. The zen
subscription is already paid for; flash consumes the balance far more
slowly than glm-5.2 did (flash cost ~$0.0000002/tok vs glm's higher rate),
so a full weekly run is much less likely to exhaust the balance — and
the operator has reset it.

Completes the fleet-wide move: upgrader parent (LOOP_MODEL) + report
(REPORT_MODEL) in upgrader.env, and this PR sets the subagents. Supervisor
stays on opencode-go/glm-5.2.

Verified: zen endpoint serves deepseek-v4-flash (HTTP 200, 1.2s).

opencode.json

@@ -2,7 +2,7 @@
   "$schema": "https://opencode.ai/config.json",
   "agent": {
     "general": {
-      "model": "tinfoil/deepseek-v4-flash"
+      "model": "opencode/deepseek-v4-flash"
     }
   }
 }