feat(deep): upgrade default model from gpt-5.3-codex to gpt-5.4

Deep category now uses gpt-5.4 as its default model across all providers
(openai, github-copilot, venice, opencode), matching Hephaestus's GPT 5.4
upgrade. The requiresModel constraint is removed since gpt-5.4 is widely
available. Adds openai/gpt-5.3-codex -> openai/gpt-5.4 config migration
for existing user configs. Deep category prompt optimized for GPT 5.4's
stronger native capabilities (leaner, less verbose).

src/tools/delegate-task/constants.ts

@@ -251,36 +251,22 @@ ANTI-AI-SLOP RULES (NON-NEGOTIABLE):
 export const DEEP_CATEGORY_PROMPT_APPEND = `<Category_Context>
 You are working on GOAL-ORIENTED AUTONOMOUS tasks.
 
-**CRITICAL - AUTONOMOUS EXECUTION MINDSET (NON-NEGOTIABLE)**:
 You are NOT an interactive assistant. You are an autonomous problem-solver.
 
-**BEFORE making ANY changes**:
-1. SILENTLY explore the codebase extensively (5-15 minutes of reading is normal)
+BEFORE making ANY changes:
+1. Silently explore the codebase extensively (5-15 minutes of reading is normal)
 2. Read related files, trace dependencies, understand the full context
 3. Build a complete mental model of the problem space
-4. DO NOT ask clarifying questions - the goal is already defined
+4. Do not ask clarifying questions - the goal is already defined
 
-**Autonomous executor mindset**:
-- You receive a GOAL. When the goal includes numbered steps or phases, treat them as one atomic task broken into sub-steps - NOT as separate independent tasks.
-- Figure out HOW to achieve the goal yourself
-- Thorough research before any action
-- Fix hairy problems that require deep understanding
-- Work independently without frequent check-ins
+You receive a GOAL. When the goal includes numbered steps or phases, treat them as one atomic task broken into sub-steps, not as separate independent tasks. Figure out HOW to achieve it yourself. Thorough research before any action.
 
-**Single vs. multi-step context**:
-- Sub-steps of ONE goal (e.g., "Step 1: analyze X, Step 2: implement Y, Step 3: test Z" for a single feature) = execute all steps, they are phases of one atomic task.
-- Genuinely independent tasks (e.g., "Task A: refactor module X" AND "Task B: fix unrelated bug Y") = flag and refuse, require separate delegations.
+Sub-steps of ONE goal = execute all steps as phases of one atomic task.
+Genuinely independent tasks = flag and refuse, require separate delegations.
 
-**Approach**:
-- Explore extensively, understand deeply, then act decisively
-- Prefer comprehensive solutions over quick patches
-- If the goal is unclear, make reasonable assumptions and proceed
-- Document your reasoning in code comments only when non-obvious
+Approach: explore extensively, understand deeply, then act decisively. Prefer comprehensive solutions over quick patches. If the goal is unclear, make reasonable assumptions and proceed.
 
-**Response format**:
-- Minimal status updates (user trusts your autonomy)
-- Focus on results, not play-by-play progress
-- Report completion with summary of changes made
+Minimal status updates. Focus on results, not play-by-play. Report completion with summary of changes.
 </Category_Context>`
 
 
@@ -288,7 +274,7 @@ You are NOT an interactive assistant. You are an autonomous problem-solver.
 export const DEFAULT_CATEGORIES: Record<string, CategoryConfig> = {
   "visual-engineering": { model: "google/gemini-3.1-pro", variant: "high" },
   ultrabrain: { model: "openai/gpt-5.4", variant: "xhigh" },
-  deep: { model: "openai/gpt-5.3-codex", variant: "medium" },
+  deep: { model: "openai/gpt-5.4", variant: "medium" },
   artistry: { model: "google/gemini-3.1-pro", variant: "high" },
   quick: { model: "openai/gpt-5.4-mini" },
   "unspecified-low": { model: "anthropic/claude-sonnet-4-6" },