chore: import upstream snapshot with attribution

cli-anything-plugin/guides/timecode-precision.md

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+# Timecode Precision
+
+Non-integer frame rates (29.97fps = 30000/1001) cause cumulative rounding errors. Follow these rules to avoid drift.
+
+## Use `round()`, Not `int()`
+
+For float-to-frame conversion:
+- `int(9000 * 29.97)` — **wrong**, truncates and loses frames
+- `round(9000 * 29.97)` — **correct**, gets the right answer
+
+## Use Integer Arithmetic for Timecode Display
+
+Convert frames → total milliseconds via:
+```python
+total_ms = round(frames * fps_den * 1000 / fps_num)
+```
+
+Then decompose with integer division. Avoid intermediate floats that drift over long durations.
+
+## Accept ±1 Frame Tolerance
+
+In roundtrip tests at non-integer FPS, exact equality is mathematically impossible. Accept ±1 frame tolerance.