feat: HTTP/2 passive fingerprinting with individual SETTINGS fields

Complete implementation of HTTP/2 passive fingerprinting per thesis §2.5.3:

mod-reqin-log (C module):
- Replace connection-level filter with ap_hook_process_connection (APR_HOOK_FIRST)
  to capture H2 preface before mod_http2 takes over the connection
- AP_MODE_SPECULATIVE read of 512 bytes from c->input_filters
- Parse SETTINGS, WINDOW_UPDATE, PRIORITY flags, pseudo-header order
- Output individual SETTINGS params as separate JSON fields (IDs 1-6, 8)
- Read H2 notes from c1 (master connection) for mod_http2 secondary conns
- Fix header_order_signature JSON length bug (26→strlen)

ClickHouse schema:
- Add 8 new columns to http_logs: h2_has_priority, h2_header_table_size,
  h2_enable_push, h2_max_concurrent_streams, h2_initial_window_size,
  h2_max_frame_size, h2_max_header_list_size, h2_enable_connect_protocol
- Use Int32/Int64 with DEFAULT -1 to distinguish absent vs zero
- Update mv_http_logs to extract individual fields via JSONHas/JSONExtractInt
- Migration 04_http2_fields.sql updated for existing deployments

Correlator:
- Accept both timestamp_ns and timestamp field names (backward compat)

Integration:
- Enable HTTP/2 in Apache: Protocols h2 http/1.1 in httpd-integration.conf

Validated end-to-end via Playwright: H2 curl traffic → mod-reqin-log →
correlator → ClickHouse with all 12 H2 columns populated correctly.

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

shared/clickhouse/06_ml_tables.sql

@@ -73,7 +73,7 @@ SETTINGS
 -- -----------------------------------------------------------------------------
 -- ml_all_scores — all classifications (no threshold, for observability)
 --
--- PARTITION BY date : TTL de 3 jours → les partitions expirées sont supprimées
+-- PARTITION BY date : TTL de 7 jours → les partitions expirées sont supprimées
 --   entièrement sans avoir à lire chaque granule (ttl_only_drop_parts).
 -- INDEX idx_detected_at : idem ml_detected_anomalies.
 -- -----------------------------------------------------------------------------
@@ -115,7 +115,7 @@ CREATE TABLE IF NOT EXISTS ja4_processing.ml_all_scores
 ENGINE = ReplacingMergeTree(detected_at)
 PARTITION BY toYYYYMMDD(window_start)
 ORDER BY (window_start, src_ip, ja4, host, model_name)
-TTL window_start + INTERVAL 3 DAY
+TTL window_start + INTERVAL 7 DAY
 SETTINGS
     index_granularity  = 8192,
     ttl_only_drop_parts = 1;