Add ruleset packs, linter, fixtures, and JSON schema

rulesets/containers.toml

@@ -0,0 +1,30 @@
+[[rule]]
+id = "MOOV_ATOM_NOT_FOUND"
+domain = "container.mp4"
+severity = "severe"
+confidence = 0.9
+fix_tier = "reencode"
+stop_scan = true
+patterns = ["(?i)moov atom not found"]
+notes = "MP4/MOV metadata is missing; file may be incomplete."
+
+[[rule]]
+id = "EBML_HEADER_PARSING_FAILED"
+domain = "container.mkv"
+severity = "high"
+confidence = 0.7
+fix_tier = "reencode"
+stop_scan = false
+patterns = ["(?i)EBML header parsing failed"]
+notes = "Matroska/WebM header parsing failed; file may be truncated."
+
+[[rule]]
+id = "FASTSTART_RECOMMENDED"
+domain = "container.mp4"
+severity = "low"
+confidence = 0.4
+fix_tier = "remux"
+stop_scan = false
+action = "faststart"
+patterns = ["(?i)faststart"]
+notes = "MP4 likely has moov atom at end; faststart remux recommended."