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/features/builtin-skills/AGENTS.md

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+# src/features/builtin-skills/ -- 8 Built-in Skills
+
+**Generated:** 2026-04-11
+
+## OVERVIEW
+
+24 files. 8 built-in skills registered via `createBuiltinSkills()`. Each skill implements `BuiltinSkill` interface with name, description, content, and optional MCP config.
+
+## STRUCTURE
+
+```
+builtin-skills/
+├── index.ts              # Barrel exports
+├── skills.ts             # createBuiltinSkills() factory
+├── types.ts              # BuiltinSkill interface
+├── git-master/           # SKILL.md + resources
+├── frontend-ui-ux/       # SKILL.md
+├── agent-browser/        # SKILL.md
+├── dev-browser/          # SKILL.md
+└── skills/               # Skill implementations as .ts files
+    ├── git-master-sections/  # Git master prompt sections
+    ├── playwright.ts         # Playwright + agent-browser + playwright-cli + dev-browser
+    ├── frontend-ui-ux.ts     # Frontend UI/UX skill
+    ├── review-work.ts        # 5-agent parallel review orchestrator
+    └── ai-slop-remover.ts    # AI code smell remover
+```
+
+## SKILL CATALOG
+
+| Skill | LOC | MCP | Purpose |
+|-------|-----|-----|---------|
+| **git-master** | 1111 | -- | Atomic commits, rebase, history search |
+| **playwright** | 312 | @playwright/mcp | Browser automation via MCP |
+| **playwright-cli** | 268 | -- | Browser automation via CLI |
+| **agent-browser** | (in playwright.ts) | -- | Browser via agent-browser tool |
+| **dev-browser** | 221 | -- | Persistent page state browser |
+| **frontend-ui-ux** | 79 | -- | Design-first UI development |
+| **review-work** | ~500 | -- | 5-agent post-implementation review |
+| **ai-slop-remover** | ~300 | -- | Remove AI code patterns |
+
+## BROWSER VARIANT SELECTION
+
+Config `browser_automation_engine` selects which browser skill loads:
+- `"playwright"` (default) -> playwright with @playwright/mcp
+- `"playwright-cli"` -> CLI-based playwright
+- `"agent-browser"` -> agent-browser tool
+
+## SKILL LOADING
+
+Skills loaded by `opencode-skill-loader` with priority: project > opencode > user > builtin. User-installed skills with same name override built-ins.