Fix sym shadowing warnings + coherent softmax gating

- Rename Init() param sym -> symName in IAgent base and overrides
  (MAAgent, MomentumAgent, RegimeADX) to stop hiding the global sym.
- Softmax gating: derive temperature from dispersion of the competence
  weights ws[] (the same quantity the softmax weights), not from the
  variance of signals zs[]; skip disabled agents in the normalization.
- Use |rho| (with weightMin floor) as competence and sign-flip
  anti-correlated agents instead of zeroing them, so rho<0 information
  is used (inverted) rather than discarded.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

MQL5/Experts/MultiAgentTest/Agents/AgentBase.mqh

@@ -37,8 +37,8 @@ public:
 
    virtual ~IAgent() {}
 
-   virtual void Init(string sym, ENUM_TIMEFRAMES tf) {
-      symbol = sym;
+   virtual void Init(string symName, ENUM_TIMEFRAMES tf) {
+      symbol = symName;
       timeframe = tf;
    }