docs: initialize project

.planning/STATE.md

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+{
+  "project_started": "2026-03-28",
+  "decisions": [
+    {
+      "date": "2026-03-28",
+      "decision": "Abandon `cv2.matchTemplate` panoramic horizon matching.",
+      "rationale": "Repeating music patterns inherently break matching systems without temporal (time-based) anchors. If measures look identical, the algorithm maps current video frames back to old identical measures causing jump-cuts and data loss.",
+      "context": "YouTube guitar tabs almost always follow a linear chronological left-to-right scrolling pattern. Only velocity tracking is needed."
+    },
+    {
+      "date": "2026-03-28",
+      "decision": "Median filtering for playhead removal.",
+      "rationale": "Animated cursors traversing horizontal staves distort matching distances and visual clarity. Using a Time-Median filter over 5-7 frames permanently erases any rapid-moving objects (like a red cursor) leaving only the static or slowly scrolling background tab notes untouched.",
+      "context": "The user approved the RAM overhead of taking multiple frames."
+    }
+  ],
+  "blockers": [],
+  "current_focus": "Phase 1: CV Core Refactor (video_cv_tracker.py)"
+}