refactor(slashcommand): split tools.ts into discovery and formatting modules

Extract slash command tool internals:
- command-discovery.ts: command finding and listing
- command-output-formatter.ts: output formatting
- skill-command-converter.ts: skill-to-command conversion
- slashcommand-description.ts: tool description generation
- slashcommand-tool.ts: core tool definition

src/tools/slashcommand/command-output-formatter.ts

@@ -0,0 +1,73 @@
+import { dirname } from "path"
+import { resolveCommandsInText, resolveFileReferencesInText } from "../../shared"
+import type { CommandInfo } from "./types"
+
+export async function formatLoadedCommand(
+  command: CommandInfo,
+  userMessage?: string
+): Promise<string> {
+  const sections: string[] = []
+
+  sections.push(`# /${command.name} Command\n`)
+
+  if (command.metadata.description) {
+    sections.push(`**Description**: ${command.metadata.description}\n`)
+  }
+
+  if (command.metadata.argumentHint) {
+    sections.push(`**Usage**: /${command.name} ${command.metadata.argumentHint}\n`)
+  }
+
+  if (userMessage) {
+    sections.push(`**Arguments**: ${userMessage}\n`)
+  }
+
+  if (command.metadata.model) {
+    sections.push(`**Model**: ${command.metadata.model}\n`)
+  }
+
+  if (command.metadata.agent) {
+    sections.push(`**Agent**: ${command.metadata.agent}\n`)
+  }
+
+  if (command.metadata.subtask) {
+    sections.push("**Subtask**: true\n")
+  }
+
+  sections.push(`**Scope**: ${command.scope}\n`)
+  sections.push("---\n")
+  sections.push("## Command Instructions\n")
+
+  let content = command.content || ""
+  if (!content && command.lazyContentLoader) {
+    content = await command.lazyContentLoader.load()
+  }
+
+  const commandDir = command.path ? dirname(command.path) : process.cwd()
+  const withFileReferences = await resolveFileReferencesInText(content, commandDir)
+  const resolvedContent = await resolveCommandsInText(withFileReferences)
+
+  let finalContent = resolvedContent.trim()
+  if (userMessage) {
+    finalContent = finalContent.replace(/\$\{user_message\}/g, userMessage)
+  }
+
+  sections.push(finalContent)
+  return sections.join("\n")
+}
+
+export function formatCommandList(items: CommandInfo[]): string {
+  if (items.length === 0) return "No commands or skills found."
+
+  const lines = ["# Available Commands & Skills\n"]
+
+  for (const command of items) {
+    const hint = command.metadata.argumentHint ? ` ${command.metadata.argumentHint}` : ""
+    lines.push(
+      `- **/${command.name}${hint}**: ${command.metadata.description || "(no description)"} (${command.scope})`
+    )
+  }
+
+  lines.push(`\n**Total**: ${items.length} items`)
+  return lines.join("\n")
+}