Refactor handlers into SRP modules and add indicator/script tools

**Handler Refactoring:**
- Split monolithic handlers.rs (1468 lines) into 7 focused modules:
  - system.rs: verify_setup, healthcheck, list_symbols
  - experts.rs: list_experts, list_indicators, list_scripts, compile_ea
  - backtest.rs: run_backtest, get_backtest_status, cache_status, clean_cache
  - optimization.rs: run_optimization, get_optimization_results, list_jobs
  - analysis.rs: analyze_report, compare_baseline
  - setfiles.rs: read/write/patch/clone/diff set files
  - reports.rs: list/search/prune reports, archive, promote, annotate

**New Tools:**
- list_indicators: List custom indicators in MQL5/Indicators
- list_scripts: List scripts in MQL5/Scripts

**Config Updates:**
- Added indicators_dir and scripts_dir to Config model
- Auto-discovery for MQL5/Indicators and MQL5/Scripts paths
- Updated healthcheck to validate new directories

**Benefits:**
- Single Responsibility Principle: each module handles one domain
- Easier maintenance and testing
- Clear separation of concerns
- Reduced cognitive load when modifying handlers

src/tools/definitions.rs

@@ -11,6 +11,8 @@ pub fn get_tools_list() -> Value {
         tool_verify_setup(),
         tool_list_symbols(),
         tool_list_experts(),
+        tool_list_indicators(),
+        tool_list_scripts(),
         tool_get_backtest_status(),
         tool_get_optimization_status(),
         tool_prune_reports(),
@@ -187,6 +189,33 @@ fn tool_list_experts() -> Value {
     })
 }
 
+fn tool_list_indicators() -> Value {
+    json!({
+        "name": "list_indicators",
+        "description": "List all custom indicators in MQL5/Indicators",
+        "inputSchema": {
+            "type": "object",
+            "properties": {
+                "filter": { "type": "string", "description": "Optional name filter pattern" },
+                "include_builtin": { "type": "boolean", "description": "Include built-in MT5 indicators", "default": false }
+            }
+        }
+    })
+}
+
+fn tool_list_scripts() -> Value {
+    json!({
+        "name": "list_scripts",
+        "description": "List all scripts in MQL5/Scripts",
+        "inputSchema": {
+            "type": "object",
+            "properties": {
+                "filter": { "type": "string", "description": "Optional name filter pattern" }
+            }
+        }
+    })
+}
+
 fn tool_get_backtest_status() -> Value {
     json!({
         "name": "get_backtest_status",