feat(agents): implement dynamic Sisyphus prompt system with agent metadata

Introduce a new dynamic prompt generation system for Sisyphus orchestrator
that leverages agent metadata for intelligent delegation. This revives the
dynamic-sisyphus-agent-prompt branch with comprehensive refactoring.

Changes:
- Add AgentPromptMetadata, AgentCategory, AgentCost, DelegationTrigger types
- Create sisyphus-prompt-builder with dynamic prompt generation logic
- Add AGENT_PROMPT_METADATA exports to all agent modules (oracle, librarian,
  explore, frontend-ui-ux-engineer, document-writer, multimodal-looker)
- Refactor sisyphus.ts to use buildDynamicSisyphusPrompt()
- Add AvailableAgent type export for type safety

This enables Sisyphus to make intelligent agent selection decisions based on
agent capabilities, costs, and delegation triggers, improving orchestration
efficiency.

🤖 Generated with assistance of OhMyOpenCode
(https://github.com/code-yeongyu/oh-my-opencode)

src/agents/document-writer.ts

@@ -1,7 +1,17 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
+import type { AgentPromptMetadata } from "./types"
 
 const DEFAULT_MODEL = "google/gemini-3-flash-preview"
 
+export const DOCUMENT_WRITER_PROMPT_METADATA: AgentPromptMetadata = {
+  category: "specialist",
+  cost: "CHEAP",
+  promptAlias: "Document Writer",
+  triggers: [
+    { domain: "Documentation", trigger: "README, API docs, guides" },
+  ],
+}
+
 export function createDocumentWriterAgent(
   model: string = DEFAULT_MODEL
 ): AgentConfig {