feat: add liquidity_sweep and price_action_reversal algorithms (#15, #16)

- Add detect_liquidity_levels() and detect_price_action_signal() to indicator_service.py
- Wire both algorithms into candle_service.py get_indicators()
- Add scoring logic and correlation groups in signal_scoring.py
- Add liquidity_sweep and price_action_reversal to STRATEGY_NAMES/DISPLAY in strategy.py
- Add funding_service.py for funding_oi algorithm (algorithm #14)
- Add rate_limiter.py for auth endpoints
- Fix: add slowapi==0.1.9 to Dockerfile
- Fix: get_db -> get_db_session in analytics.py
- Fix: remove from __future__ import annotations in auth.py

System now runs 16 algorithms: 13 original + funding_oi + liquidity_sweep + price_action_reversal

backend/app/core/rate_limiter.py

@@ -0,0 +1,67 @@
+"""Rate limiting for authentication endpoints using slowapi."""
+
+import time
+from collections import defaultdict
+from typing import Optional
+
+from slowapi import Limiter
+from slowapi.util import get_remote_address
+
+limiter = Limiter(key_func=get_remote_address)
+
+# Rate limit configurations
+AUTH_RATE_LIMIT = "5/15minutes"  # 5 failures in 15 minutes
+REGISTER_RATE_LIMIT = "3/hour"
+
+# Track failed login attempts per IP address
+# Format: {ip_address: [(timestamp, reason), ...]}
+_failed_attempts: dict[str, list[tuple[float, str]]] = defaultdict(list)
+_FAILURE_LOCKOUT_DURATION = 900  # 15 minutes in seconds
+_MAX_FAILURES = 5
+_FAILURE_WINDOW = 900  # 15 minute window
+
+
+def record_failed_login(ip_address: str, reason: str = "invalid_credentials") -> None:
+    """Record a failed login attempt. After 5 failures in 15min, returns locked state."""
+    current_time = time.time()
+    _failed_attempts[ip_address].append((current_time, reason))
+    
+    # Clean up old attempts outside the window
+    _failed_attempts[ip_address] = [
+        (ts, reason) for ts, reason in _failed_attempts[ip_address]
+        if current_time - ts < _FAILURE_WINDOW
+    ]
+
+
+def is_login_locked(ip_address: str) -> tuple[bool, Optional[int]]:
+    """Check if an IP is locked due to too many failed attempts.
+    
+    Returns: (is_locked, seconds_until_unlock)
+    """
+    if ip_address not in _failed_attempts:
+        return False, None
+    
+    current_time = time.time()
+    
+    # Clean up old attempts
+    _failed_attempts[ip_address] = [
+        (ts, reason) for ts, reason in _failed_attempts[ip_address]
+        if current_time - ts < _FAILURE_WINDOW
+    ]
+    
+    attempts = _failed_attempts[ip_address]
+    
+    if len(attempts) >= _MAX_FAILURES:
+        # Calculate when the oldest failure expires
+        oldest_failure = min(ts for ts, _ in attempts)
+        unlock_time = oldest_failure + _FAILURE_WINDOW
+        seconds_until_unlock = max(0, int(unlock_time - current_time))
+        return True, seconds_until_unlock
+    
+    return False, None
+
+
+def clear_failed_attempts(ip_address: str) -> None:
+    """Clear failed login attempts for an IP (successful login)."""
+    if ip_address in _failed_attempts:
+        del _failed_attempts[ip_address]