refactor: remove MCP code-index dependency, replace with ripgrep/find

Replace all mcp__code-index__ calls with native ripgrep and find commands
across workflow and command files for better performance and portability.

Changes:
- Remove 41 mcp__code-index__ function calls from 12 files
- Replace with ripgrep (rg) for content search
- Replace with find for file discovery
- Remove index refresh dependencies (no longer needed)

Modified files:
- workflow/tools: context-gather, test-context-gather, task-generate-agent,
  task-generate, test-task-generate (core workflow tools)
- workflow: review (security scanning)
- memory: load, update-related, docs (memory management)
- cli/mode: plan, bug-index, code-analysis (CLI modes)

Documentation updates:
- Simplify mcp-tool-strategy.md to only Exa usage (5 lines)
- Streamline context-search-strategy.md to 69 lines
- Standardize codebase-retrieval syntax per intelligent-tools-strategy.md

Benefits:
- Faster search with ripgrep (no index overhead)
- Better cross-platform compatibility
- Simpler configuration (fewer MCP dependencies)
- -232 lines of code removed

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

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

.claude/commands/workflow/tools/task-generate.md

@@ -249,9 +249,9 @@ This enhanced 5-field schema embeds all necessary context, artifacts, and execut
         }
       },
       {
-        "step": "mcp_codebase_exploration",
-        "action": "Explore codebase using MCP tools",
-        "command": "mcp__code-index__find_files(pattern=\"[patterns]\") && mcp__code-index__search_code_advanced(pattern=\"[patterns]\")",
+        "step": "codebase_exploration",
+        "action": "Explore codebase using native tools",
+        "command": "bash(find . -name \"[patterns]\" -type f && rg \"[patterns]\")",
         "output_to": "codebase_structure"
       },
       {