Reorganize tool definitions into granular domain modules

**New structure:**
src/tools/definitions/
├── mod.rs         # Aggregates all 43 tools
├── system.rs      # 3 tools: healthcheck, verify_setup, list_symbols
├── experts.rs     # 4 tools: compile_ea, list_experts, list_indicators, list_scripts
├── backtest.rs    # 4 tools: run_backtest, get_backtest_status, cache_status, clean_cache
├── optimization.rs # 4 tools: run_optimization, get_optimization_status, get_optimization_results, list_jobs
├── analytics.rs   # 9 tools: analyze_report + 8 granular analytics
├── reports.rs     # 11 tools: list_reports, search_reports, get_latest_report, etc.
├── setfiles.rs    # 8 tools: read/write/patch/clone/diff set files
└── baseline.rs    # 1 tool: compare_baseline

**Benefits:**
- Domain-based organization (21KB monolith -> 9 focused files)
- Each domain can evolve independently
- Easier to find and modify tool definitions
- Clear separation between system, experts, backtest, optimization, analytics, reports, setfiles

src/tools/definitions/system.rs

@@ -0,0 +1,37 @@
+use serde_json::{json, Value};
+
+pub fn tool_healthcheck() -> Value {
+    json!({
+        "name": "healthcheck",
+        "description": "System health check with OS detection and configuration validation",
+        "inputSchema": {
+            "type": "object",
+            "properties": {
+                "detailed": { "type": "boolean", "description": "Include detailed system info", "default": false }
+            }
+        }
+    })
+}
+
+pub fn tool_verify_setup() -> Value {
+    json!({
+        "name": "verify_setup",
+        "description": "Validate MT5-Quant environment configuration",
+        "inputSchema": {
+            "type": "object"
+        }
+    })
+}
+
+pub fn tool_list_symbols() -> Value {
+    json!({
+        "name": "list_symbols",
+        "description": "List symbols with local tick history",
+        "inputSchema": {
+            "type": "object",
+            "properties": {
+                "server": { "type": "string" }
+            }
+        }
+    })
+}