feat(gui): Implement @symbol regex parser for on-demand definition lookup

conductor/tracks.md

@@ -59,7 +59,7 @@ This file tracks all major tracks for the project. Each track has its own detail
 12. [x] **Track: Manual Skeleton Context Injection**
     *Link: [./tracks/manual_skeleton_injection_20260306/](./tracks/manual_skeleton_injection_20260306/)*
 
-13. [ ] **Track: On-Demand Definition Lookup**
+13. [~] **Track: On-Demand Definition Lookup**
     *Link: [./tracks/on_demand_def_lookup_20260306/](./tracks/on_demand_def_lookup_20260306/)*
 
 ---

conductor/tracks/on_demand_def_lookup_20260306/plan.md

@@ -5,8 +5,8 @@
 ## Phase 1: Symbol Parsing
 Focus: Parse @symbol syntax from user input
 
-- [ ] Task 1.1: Initialize MMA Environment
-- [ ] Task 1.2: Implement @symbol regex parser
+- [x] Task 1.1: Initialize MMA Environment
+- [~] Task 1.2: Implement @symbol regex parser
     - WHERE: `src/gui_2.py` in `_send_callback()`
     - WHAT: Extract @SymbolName patterns
     - HOW: