feat: add incremental log scanning with resumable byte offsets

Track last processed byte offset per log file so scans only read new
entries, add --full flag to force a rescan, and persist state atomically.

reports/app/data/blocklist_ipv4.txt

@@ -38,6 +38,7 @@
 118.212.120.78/32
 118.81.196.142/32
 118.81.207.202/32
+121.29.51.109/32
 123.158.61.179/32
 123.160.175.254/32
 123.163.114.150/32
@@ -343,6 +344,7 @@
 34.17.159.73/32
 34.171.75.208/32
 34.175.82.8/32
+34.176.154.83/32
 34.18.38.137/32
 34.181.134.189/32
 34.186.83.134/32