Add ruleset packs, linter, fixtures, and JSON schema

rulesets/codecs-video.toml

@@ -0,0 +1,39 @@
+[[rule]]
+id = "INVALID_NAL_UNIT_SIZE"
+domain = "codec.h264"
+severity = "severe"
+confidence = 0.85
+fix_tier = "reencode"
+stop_scan = true
+patterns = ["(?i)Invalid NAL unit size", "(?i)Error splitting the input into NAL units"]
+notes = "H.264/HEVC bitstream corruption detected."
+
+[[rule]]
+id = "MISSING_PICTURE_ACCESS_UNIT"
+domain = "codec.h264"
+severity = "high"
+confidence = 0.7
+fix_tier = "reencode"
+stop_scan = false
+patterns = ["(?i)missing picture in access unit"]
+notes = "Missing picture in access unit; possible corruption."
+
+[[rule]]
+id = "PPS_ID_OUT_OF_RANGE"
+domain = "codec.hevc"
+severity = "high"
+confidence = 0.75
+fix_tier = "reencode"
+stop_scan = false
+patterns = ["(?i)PPS id out of range", "(?i)Error parsing NAL unit"]
+notes = "HEVC parameter set corruption detected."
+
+[[rule]]
+id = "SEI_TRUNCATED"
+domain = "codec.h264"
+severity = "low"
+confidence = 0.5
+fix_tier = "none"
+stop_scan = false
+patterns = ["(?i)SEI type .* truncated"]
+notes = "SEI message truncated; often benign unless paired with decode errors."