refactor: suppression dépendance User-Agent de la détection navigateur

Changements SQL :
- modern_browser_score : sec-ch-ua→100, Sec-Fetch→70 (plus de UA fallback)
- Ajout has_sec_ch_ua (UInt8) dans agg_header_fingerprint_1h et ml_all_scores
- mss_mobile_mismatch utilise has_sec_ch_ua au lieu de modern_browser_score
- header_order_confidence : PARTITION BY ja4 au lieu de first_ua
- sec_ch_mobile_mismatch : comparaison Client Hints interne (sans UA)
- Migration 03_remove_ua_browser_detection.sql

Changements Python :
- browser.py Axe 3 : Client Hints + Sec-Fetch + is_fake_navigation (PAS de UA)
- Pondération axes : ja4_known 0.30, tls_coherence 0.20 (signaux TLS renforcés)
- preprocessing.py : has_sec_ch_ua ajouté aux features et binary_features

Fichiers modifiés : 8 SQL/Python + 1 migration, 36/36 tests passent.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

services/bot-detector/bot_detector/preprocessing.py

@@ -20,7 +20,7 @@ FEATURES = [
     'hits', 'hit_velocity', 'fuzzing_index', 'post_ratio', 'port_exhaustion_ratio',
     'orphan_ratio', 'max_keepalives', 'tcp_shared_count', 'header_order_shared_count',
     'header_count', 'has_accept_language', 'has_cookie', 'has_referer',
-    'modern_browser_score', 'ua_ch_mismatch', 'ip_id_zero_ratio',
+    'modern_browser_score', 'ua_ch_mismatch', 'has_sec_ch_ua', 'ip_id_zero_ratio',
     'request_size_variance', 'multiplexing_efficiency', 'mss_mobile_mismatch',
     'asset_ratio', 'direct_access_ratio', 'is_ua_rotating', 'distinct_ja4_count',
     'src_port_density', 'ja4_asn_concentration', 'ja4_country_concentration', 'is_rare_ja4',
@@ -103,7 +103,8 @@ def preprocess_df(df: pd.DataFrame) -> pd.DataFrame:
 
     # Imputation intelligente
     binary_features = {
-        'has_accept_language', 'has_cookie', 'has_referer', 'ua_ch_mismatch',
+        'has_accept_language', 'has_cookie', 'has_referer', 'has_sec_ch_ua',
+        'ua_ch_mismatch',
         'is_ua_rotating', 'is_alpn_missing', 'sni_host_mismatch', 'alpn_http_mismatch',
         'mss_mobile_mismatch', 'anubis_is_flagged', 'is_rare_ja4',
         'is_fake_navigation', 'has_xff', 'sec_ch_mobile_mismatch',