feat(categories): change quick category default model from claude-haiku-4-5 to gpt-5.4-mini

GPT-5.4-mini provides stronger reasoning at comparable speed and cost.
Haiku remains as the next fallback priority in the chain.

Changes:
- DEFAULT_CATEGORIES quick model: anthropic/claude-haiku-4-5 → openai/gpt-5.4-mini
- Fallback chain: gpt-5.4-mini → haiku → gemini-3-flash → minimax-m2.5 → gpt-5-nano
- OpenAI-only catalog: quick uses gpt-5.4-mini directly
- Think-mode: add gpt-5-4-mini and gpt-5-4-nano high variants
- Update all documentation references

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

@@ -248,8 +248,7 @@ exports[`generateModelConfig single native provider uses OpenAI models when only
       "variant": "medium",
     },
     "quick": {
-      "model": "openai/gpt-5.3-codex",
-      "variant": "low",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -334,8 +333,7 @@ exports[`generateModelConfig single native provider uses OpenAI models with isMa
       "variant": "medium",
     },
     "quick": {
-      "model": "openai/gpt-5.3-codex",
-      "variant": "low",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -533,7 +531,7 @@ exports[`generateModelConfig all native providers uses preferred models from fal
       "variant": "medium",
     },
     "quick": {
-      "model": "anthropic/claude-haiku-4-5",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -608,7 +606,7 @@ exports[`generateModelConfig all native providers uses preferred models with isM
       "variant": "medium",
     },
     "quick": {
-      "model": "anthropic/claude-haiku-4-5",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -684,7 +682,7 @@ exports[`generateModelConfig fallback providers uses OpenCode Zen models when on
       "variant": "medium",
     },
     "quick": {
-      "model": "opencode/claude-haiku-4-5",
+      "model": "opencode/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "opencode/gpt-5.4",
@@ -759,7 +757,7 @@ exports[`generateModelConfig fallback providers uses OpenCode Zen models with is
       "variant": "medium",
     },
     "quick": {
-      "model": "opencode/claude-haiku-4-5",
+      "model": "opencode/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "opencode/gpt-5.4",
@@ -830,7 +828,7 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models when
       "variant": "high",
     },
     "quick": {
-      "model": "github-copilot/claude-haiku-4.5",
+      "model": "github-copilot/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "github-copilot/gemini-3.1-pro-preview",
@@ -900,7 +898,7 @@ exports[`generateModelConfig fallback providers uses GitHub Copilot models with
       "variant": "high",
     },
     "quick": {
-      "model": "github-copilot/claude-haiku-4.5",
+      "model": "github-copilot/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "github-copilot/gemini-3.1-pro-preview",
@@ -1092,7 +1090,7 @@ exports[`generateModelConfig mixed provider scenarios uses Claude + OpenCode Zen
       "variant": "medium",
     },
     "quick": {
-      "model": "anthropic/claude-haiku-4-5",
+      "model": "opencode/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "opencode/gpt-5.4",
@@ -1167,7 +1165,7 @@ exports[`generateModelConfig mixed provider scenarios uses OpenAI + Copilot comb
       "variant": "medium",
     },
     "quick": {
-      "model": "github-copilot/claude-haiku-4.5",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -1375,7 +1373,7 @@ exports[`generateModelConfig mixed provider scenarios uses all fallback provider
       "variant": "medium",
     },
     "quick": {
-      "model": "github-copilot/claude-haiku-4.5",
+      "model": "github-copilot/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "opencode/gpt-5.4",
@@ -1453,7 +1451,7 @@ exports[`generateModelConfig mixed provider scenarios uses all providers togethe
       "variant": "medium",
     },
     "quick": {
-      "model": "anthropic/claude-haiku-4-5",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",
@@ -1531,7 +1529,7 @@ exports[`generateModelConfig mixed provider scenarios uses all providers with is
       "variant": "medium",
     },
     "quick": {
-      "model": "anthropic/claude-haiku-4-5",
+      "model": "openai/gpt-5.4-mini",
     },
     "ultrabrain": {
       "model": "openai/gpt-5.4",