fix(commands): make ace-tool MCP optional in multi-* commands with built-in fallbacks

The multi-* commands (multi-plan, multi-execute, multi-workflow, multi-backend,
multi-frontend) previously required ace-tool MCP (Augment Code) which is a paid
service. This change makes ace-tool completely optional by:

- Changing "MUST call" to "If ace-tool MCP is available" for enhance_prompt
- Changing mandatory search_context calls to optional with fallback procedures
- Adding detailed fallback instructions using Claude Code built-in tools
  (Glob, Grep, Read, Task/Explore agent) when ace-tool is unavailable
- Updating all translations (ja-JP, zh-CN) to match

This ensures multi-* commands work out of the box without ace-tool MCP configured.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

commands/multi-execute.md

@@ -136,7 +136,7 @@ TaskOutput({ task_id: "<task_id>", block: true, timeout: 600000 })
 
 `[Mode: Retrieval]`
 
-**Must use MCP tool for quick context retrieval, do NOT manually read files one by one**
+**If ace-tool MCP is available**, use it for quick context retrieval:
 
 Based on "Key Files" list in plan, call `mcp__ace-tool__search_context`:
 
@@ -151,7 +151,12 @@ mcp__ace-tool__search_context({
 - Extract target paths from plan's "Key Files" table
 - Build semantic query covering: entry files, dependency modules, related type definitions
 - If results insufficient, add 1-2 recursive retrievals
-- **NEVER** use Bash + find/ls to manually explore project structure
+
+**If ace-tool MCP is NOT available**, use Claude Code built-in tools as fallback:
+1. **Glob**: Find target files from plan's "Key Files" table (e.g., `Glob("src/components/**/*.tsx")`)
+2. **Grep**: Search for key symbols, function names, type definitions across the codebase
+3. **Read**: Read the discovered files to gather complete context
+4. **Task (Explore agent)**: For broader exploration, use `Task` with `subagent_type: "Explore"`
 
 **After Retrieval**:
 - Organize retrieved code snippets