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>

shared/clickhouse/06_ml_tables.sql

@@ -33,7 +33,8 @@ CREATE TABLE IF NOT EXISTS ja4_processing.ml_detected_anomalies
     tcp_jitter_variance Float32, tcp_shared_count UInt32, true_window_size UInt64,
     window_mss_ratio Float32, alpn_http_mismatch UInt8, is_alpn_missing UInt8,
     sni_host_mismatch UInt8, header_count UInt16, has_accept_language UInt8,
-    has_cookie UInt8, has_referer UInt8, modern_browser_score UInt8, is_headless UInt8,
+    has_cookie UInt8, has_referer UInt8, modern_browser_score UInt8, has_sec_ch_ua UInt8,
+    is_headless UInt8,
     ua_ch_mismatch UInt8, header_order_shared_count UInt32, ip_id_zero_ratio Float32,
     request_size_variance Float32, multiplexing_efficiency Float32,
     mss_mobile_mismatch UInt8, correlated UInt8, reason String,