fix: clearer no-signal reason + cp1252 unicode crash in logger

- mt5_trader: replace generic "No signal (need >X or <Y)" with an
  explicit reason that names the actual block — regime mismatch vs
  probability not cleared (e.g. "Bear state but prob=0.521 not <0.480")
  so users can see at a glance whether the HMM or XGBoost gated the bar
- main: replace U+2192 arrow in migration log message with ASCII '->'
  to avoid UnicodeEncodeError on Windows cp1252 terminals

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.py

@@ -58,7 +58,7 @@ def _check_m5_readiness(tf: str, broker: str = "headway_cent") -> bool:
         _legacy = Path("models/m5_meta.json")
         if _legacy.exists():
             logger.info(
-                "Migrating legacy m5_meta.json → %s for broker=%s.", meta_path, broker
+                "Migrating legacy m5_meta.json -> %s for broker=%s.", meta_path, broker
             )
             meta_path.write_text(_legacy.read_text())
         else:

src/mt5_trader.py

@@ -844,10 +844,14 @@ def _run_loop_inner(tf: str, broker: str, account_size: float, mt5,
                 direction  = "SELL"
                 order_type = mt5.ORDER_TYPE_SELL
             else:
-                logger.info(
-                    "No signal (prob=%.3f  state=%s  need >%.3f or <%.3f).",
-                    prob, state_lbl, prob_threshold, short_threshold,
-                )
+                # Explain exactly why no signal fired
+                if hmm_state == BULL_STATE:
+                    reason = f"Bull state but prob={prob:.3f} not >{prob_threshold:.3f}"
+                elif hmm_state == BEAR_STATE:
+                    reason = f"Bear state but prob={prob:.3f} not <{short_threshold:.3f}"
+                else:
+                    reason = f"Chop state — no signal regardless of prob"
+                logger.info("No signal (%s).", reason)
                 time.sleep(POLL_INTERVAL_SEC)
                 continue