feat(model-requirements): set multimodal-looker primary model to gpt-5.4 medium

Change multimodal-looker's primary model from gpt-5.3-codex to gpt-5.4 medium
in both runtime and CLI fallback chains.

Changes:
- Runtime chain (src/shared/model-requirements.ts): primary now gpt-5.4
- CLI chain (src/cli/model-fallback-requirements.ts): primary now gpt-5.4
- Updated test expectations in model-requirements.test.ts
- Updated config-manager.test.ts assertion
- Updated model-fallback snapshots

src/cli/__snapshots__/model-fallback.test.ts.snap

@@ -213,7 +213,7 @@ exports[`generateModelConfig single native provider uses OpenAI models when only
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -286,7 +286,7 @@ exports[`generateModelConfig single native provider uses OpenAI models with isMa
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -480,7 +480,7 @@ exports[`generateModelConfig all native providers uses preferred models from fal
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -555,7 +555,7 @@ exports[`generateModelConfig all native providers uses preferred models with isM
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -631,7 +631,7 @@ exports[`generateModelConfig fallback providers uses OpenCode Zen models when on
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "opencode/gpt-5.3-codex",
+      "model": "opencode/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -706,7 +706,7 @@ exports[`generateModelConfig fallback providers uses OpenCode Zen models with is
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "opencode/gpt-5.3-codex",
+      "model": "opencode/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -1025,7 +1025,7 @@ exports[`generateModelConfig mixed provider scenarios uses Claude + OpenCode Zen
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "opencode/gpt-5.3-codex",
+      "model": "opencode/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -1100,7 +1100,7 @@ exports[`generateModelConfig mixed provider scenarios uses OpenAI + Copilot comb
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -1302,7 +1302,7 @@ exports[`generateModelConfig mixed provider scenarios uses all fallback provider
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "opencode/gpt-5.3-codex",
+      "model": "opencode/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -1377,7 +1377,7 @@ exports[`generateModelConfig mixed provider scenarios uses all providers togethe
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {
@@ -1452,7 +1452,7 @@ exports[`generateModelConfig mixed provider scenarios uses all providers with is
       "variant": "xhigh",
     },
     "multimodal-looker": {
-      "model": "openai/gpt-5.3-codex",
+      "model": "openai/gpt-5.4",
       "variant": "medium",
     },
     "oracle": {