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/skill-command-converter.ts

@@ -0,0 +1,20 @@
+import type { LoadedSkill } from "../../features/opencode-skill-loader"
+import type { CommandInfo } from "./types"
+
+export function skillToCommandInfo(skill: LoadedSkill): CommandInfo {
+  return {
+    name: skill.name,
+    path: skill.path,
+    metadata: {
+      name: skill.name,
+      description: skill.definition.description || "",
+      argumentHint: skill.definition.argumentHint,
+      model: skill.definition.model,
+      agent: skill.definition.agent,
+      subtask: skill.definition.subtask,
+    },
+    content: skill.definition.template,
+    scope: skill.scope,
+    lazyContentLoader: skill.lazyContent,
+  }
+}