feat(dispatch): wire marketplace plugin commands into slash command dispatch

Connect the existing plugin loader infrastructure to both slash command
dispatch paths (executor and slashcommand tool), enabling namespaced
commands like /daplug:run-prompt to resolve and execute.

- Add plugin discovery to executor.ts discoverAllCommands()
- Add plugin discovery to command-discovery.ts discoverCommandsSync()
- Add "plugin" to CommandScope type
- Remove blanket colon-rejection error (replaced with standard not-found)
- Update slash command regex to accept namespaced commands
- Thread claude_code.plugins config toggle through dispatch chain
- Add unit tests for plugin command discovery and dispatch

Closes #2019

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Codex <noreply@openai.com>

src/tools/skill/tools.ts

@@ -16,6 +16,7 @@ const scopePriority: Record<string, number> = {
   user: 3,
   opencode: 2,
   "opencode-project": 2,
+  plugin: 1,
   config: 1,
   builtin: 1,
 }
@@ -89,7 +90,7 @@ function formatCombinedDescription(skills: SkillInfo[], commands: CommandInfo[])
   }
 
   if (allItems.length > 0) {
-    lines.push(`\n<available_items>\nPriority: project > user > opencode > builtin | Skills listed before commands\nInvoke via: skill(name="item-name") — omit leading slash for commands.\n${allItems.join("\n")}\n</available_items>`)
+    lines.push(`\n<available_items>\nPriority: project > user > opencode > builtin/plugin | Skills listed before commands\nInvoke via: skill(name="item-name") — omit leading slash for commands.\n${allItems.join("\n")}\n</available_items>`)
   }
 
   return TOOL_DESCRIPTION_PREFIX + lines.join("")
@@ -195,7 +196,10 @@ export function createSkillTool(options: SkillLoadOptions = {}): ToolDefinition
 
   const getCommands = (): CommandInfo[] => {
     if (cachedCommands) return cachedCommands
-    cachedCommands = discoverCommandsSync()
+    cachedCommands = discoverCommandsSync(undefined, {
+      pluginsEnabled: options.pluginsEnabled,
+      enabledPluginsOverride: options.enabledPluginsOverride,
+    })
     return cachedCommands
   }