feat(models): promote gpt-5.5 as default for oracle, hephaestus, and deep

Now that each of these agents ships a native gpt-5.5 prompt variant,
their default OpenAI model is bumped from gpt-5.4 to gpt-5.5. The
gpt-5.4 entries are removed from the same-provider position in each
fallback chain (a single provider doesn't need both version entries -
if gpt-5.5 isn't available there, cross-provider fallback kicks in).

- oracle.fallbackChain: gpt-5.5 high (openai) -> gemini-3.1-pro -> claude -> glm
- hephaestus.fallbackChain: gpt-5.5 medium (openai only, requiresProvider)
- deep category.fallbackChain: gpt-5.5 medium -> claude -> gemini
- deep category.config: openai/gpt-5.5 medium

No changes to sisyphus, sisyphus-junior, ultrabrain, momus, or other
agents that still point at gpt-5.4; those stay on the shared regex-
based routing in the gpt-5-4 prompt family.

src/shared/model-requirements.ts

@@ -49,7 +49,7 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
     fallbackChain: [
       {
         providers: ["openai", "github-copilot", "venice", "opencode", "vercel"],
-        model: "gpt-5.4",
+        model: "gpt-5.5",
         variant: "medium",
       },
     ],
@@ -59,7 +59,7 @@ export const AGENT_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
     fallbackChain: [
       {
         providers: ["openai", "github-copilot", "opencode", "vercel"],
-        model: "gpt-5.4",
+        model: "gpt-5.5",
         variant: "high",
       },
       {
@@ -225,7 +225,7 @@ export const CATEGORY_MODEL_REQUIREMENTS: Record<string, ModelRequirement> = {
     fallbackChain: [
       {
         providers: ["openai", "github-copilot", "venice", "opencode", "vercel"],
-        model: "gpt-5.4",
+        model: "gpt-5.5",
         variant: "medium",
       },
       {

src/tools/delegate-task/openai-categories.ts

@@ -103,7 +103,7 @@ export const OPENAI_CATEGORIES: BuiltinCategoryDefinition[] = [
   },
   {
     name: "deep",
-    config: { model: "openai/gpt-5.4", variant: "medium" },
+    config: { model: "openai/gpt-5.5", variant: "medium" },
     description: "Goal-oriented autonomous problem-solving. Thorough research before action. For hairy problems requiring deep understanding.",
     promptAppend: DEEP_CATEGORY_PROMPT_APPEND,
   },