Add centralized constants module and .env configuration support

app/flags.py

@@ -7,11 +7,12 @@ Detection functions that identify hostile IPs based on aggregated stats.
 from __future__ import annotations
 
 from . import bad_patterns
+from .constants import DEFAULT_ERROR_RATIO, DEFAULT_MIN_DENIED, DEFAULT_MIN_ERRORS
 from .models import IPStats
 
 
-def flag_scanners(stats: dict[str, IPStats], min_errors: int = 5,
-                  min_ratio: float = 0.5) -> dict[str, IPStats]:
+def flag_scanners(stats: dict[str, IPStats], min_errors: int = DEFAULT_MIN_ERRORS,
+                  min_ratio: float = DEFAULT_ERROR_RATIO) -> dict[str, IPStats]:
     """IPs with many errors AND a high error ratio."""
     return {
         ip: s for ip, s in stats.items()
@@ -20,7 +21,7 @@ def flag_scanners(stats: dict[str, IPStats], min_errors: int = 5,
 
 
 def flag_denied_only(stats: dict[str, IPStats],
-                     min_denied: int = 1) -> dict[str, IPStats]:
+                     min_denied: int = DEFAULT_MIN_DENIED) -> dict[str, IPStats]:
     """IPs that only ever hit denied paths and never authenticated."""
     return {
         ip: s for ip, s in stats.items()