fix(skill): unify skill resolution to support user custom skills

sisyphus_task was only loading builtin skills via resolveMultipleSkills().
Now uses resolveMultipleSkillsAsync() which merges discoverSkills() + builtin skills.

- Add getAllSkills(), extractSkillTemplate(), resolveMultipleSkillsAsync()
- Update sisyphus_task to use async skill resolution
- Refactor skill tool to reuse unified getAllSkills()
- Add async skill resolution tests

src/tools/skill/tools.ts

@@ -1,10 +1,9 @@
 import { dirname } from "node:path"
-import { readFileSync } from "node:fs"
 import { tool, type ToolDefinition } from "@opencode-ai/plugin"
 import { TOOL_DESCRIPTION_NO_SKILLS, TOOL_DESCRIPTION_PREFIX } from "./constants"
 import type { SkillArgs, SkillInfo, SkillLoadOptions } from "./types"
-import { discoverSkills, type LoadedSkill } from "../../features/opencode-skill-loader"
-import { parseFrontmatter } from "../../shared/frontmatter"
+import type { LoadedSkill } from "../../features/opencode-skill-loader"
+import { getAllSkills, extractSkillTemplate } from "../../features/opencode-skill-loader/skill-content"
 import type { SkillMcpManager, SkillMcpClientInfo, SkillMcpServerContext } from "../../features/skill-mcp-manager"
 import type { Tool, Resource, Prompt } from "@modelcontextprotocol/sdk/types.js"
 
@@ -48,9 +47,7 @@ async function extractSkillBody(skill: LoadedSkill): Promise<string> {
   }
 
   if (skill.path) {
-    const content = readFileSync(skill.path, "utf-8")
-    const { body } = parseFrontmatter(content)
-    return body.trim()
+    return extractSkillTemplate(skill)
   }
 
   const templateMatch = skill.definition.template?.match(/<skill-instruction>([\s\S]*?)<\/skill-instruction>/)
@@ -135,7 +132,7 @@ export function createSkillTool(options: SkillLoadOptions = {}): ToolDefinition
   const getSkills = async (): Promise<LoadedSkill[]> => {
     if (options.skills) return options.skills
     if (cachedSkills) return cachedSkills
-    cachedSkills = await discoverSkills({ includeClaudeCodePaths: !options.opencodeOnly })
+    cachedSkills = await getAllSkills()
     return cachedSkills
   }