docs(agents): add AGENTS.md documentation for prometheus, hephaestus, sisyphus variants, and builtin-skills

- src/agents/prometheus/: Strategic planner documentation
- src/agents/hephaestus/: GPT-5.4 autonomous worker documentation
- src/agents/sisyphus/: Model-specific orchestrator variants documentation
- src/features/builtin-skills/: 8 built-in skills catalog

🤖 Generated with OhMyOpenCode assistance

src/agents/hephaestus/AGENTS.md

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+# src/agents/hephaestus/ -- Autonomous Deep Worker
+
+**Generated:** 2026-04-11
+
+## OVERVIEW
+
+6 files. Hephaestus agent -- autonomous deep worker powered by GPT-5.4. Goal-oriented: give it objectives, not step-by-step instructions. "The Legitimate Craftsman."
+
+## FILES
+
+| File | Purpose |
+|------|---------|
+| `agent.ts` | `createHephaestusAgent()` factory, model-variant routing |
+| `gpt.ts` | Base GPT prompt: discipline rules, delegation, verification |
+| `gpt-5-4.ts` | GPT-5.4-native prompt with XML-tagged blocks, entropy-reduced |
+| `gpt-5-3-codex.ts` | GPT-5.3 Codex variant with task discipline sections |
+| `index.ts` | Barrel exports |
+
+## KEY BEHAVIORS
+
+- Mode: `primary` (respects UI model selection)
+- Requires OpenAI-compatible provider (no fallback chain)
+- NEVER trusts subagent self-reports -- always verifies
+- NEVER uses `background_cancel(all=true)`
+- Delegates exploration to background agents, never sequential
+- Uses `run_in_background=true` for explore/librarian
+
+## MODEL VARIANTS
+
+| Model | Prompt Source | Optimizations |
+|-------|-------------|---------------|
+| gpt-5.4 | `gpt-5-4.ts` | XML-tagged blocks, 8 sections |
+| gpt-5.3-codex | `gpt-5-3-codex.ts` | Task discipline, 549 LOC prompt |
+| Other GPT | `gpt.ts` | Base prompt, 507 LOC |