chore(pi): bump default model to gpt-6-luna and retune subagents

Drop gpt-5.6-luna across the default and reviewer/oracle overrides in
favour of gpt-6-luna, and move the planner to deepseek-v4-pro. Also
raise reviewer thinking to high and drop the now-unneeded
fallbackModels entries since the primary targets resolve.

config/pi/agent/settings.json

@@ -1,8 +1,8 @@
 {
     "lastChangelogVersion": "0.99.2",
     "theme": "light/dark",
-  "defaultProvider": "obelix",
+    "defaultProvider": "openai-codex",
-  "defaultModel": "ornith-1.5-35B",
+    "defaultModel": "gpt-6-luna",
     "defaultThinkingLevel": "high",
     "hideThinkingBlock": true,
     "compaction": {
@@ -30,28 +30,24 @@
     "subagents": {
         "agentOverrides": {
             "reviewer": {
-        "model": "obelix/ornith-1.5-35B",
+                "model": "openai-codex/gpt-6-luna",
-        "fallbackModels": [
+                "thinking": "high"
-          "openai-codex/gpt-6-luna"
-        ],
-        "thinking": "low"
             },
             "planner": {
-        "model": "opencode-go/gpt-6-luna"
+                "model": "opencode-go/deepseek-v4-pro"
             },
             "worker": {
-        "model": "obelix/ornith-1.5-35B"
+                "model": "obelix/ornith-1.0-35B"
             },
             "oracle": {
-        "model": "openai-codex/gpt-6-luna",
+                "model": "openai-codex/gpt-6.1-sol",
-        "fallbackModels": [
-          "opencode-go/qwen3.7-max"
-        ],
                 "thinking": "high"
             }
         }
     },
-  "defaultTools": ["+codemode"],
+    "defaultTools": [
+        "+codemode"
+    ],
     "quietStartup": true,
     "steeringMode": "all",
     "terminal": {