Feat: documentation, UI/UX

docs/tutorials/periodic_script.md

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+# The Periodic Script
+
+The periodic script is a hidden seventh view accessible with `F11`. It is a Forth script that runs continuously alongside your patterns, evaluated at every step like a pattern would be. Think of it as a free-running pattern with no grid — just code.
+
+## What is it for?
+
+The periodic script is useful for things that don't belong to any specific pattern:
+
+- **Global effects**: apply a filter sweep or reverb tail across everything.
+- **Drones**: run a sustained sound that keeps going regardless of which patterns are playing.
+- **Control logic**: update variables, send MIDI clock, or modulate global parameters.
+- **Experimentation**: sketch ideas without touching your pattern grid.
+
+## Opening the Script
+
+Press `F11` from any view. The script page appears with an editor on the left and visualizations on the right (scope, spectrum, prelude preview). The script is saved with your project.
+
+## Editing
+
+Press `Enter` to focus the editor. Write Forth code as you would in any step. Press `Esc` to unfocus and save. Press `Ctrl+E` to evaluate without unfocusing.
+
+```forth
+;; a simple drone
+saw s c2 note 0.3 gain 0.4 verb .
+```
+
+## Speed and Length
+
+The periodic script has its own speed and length settings, independent of any pattern. Press `S` (unfocused) to set the speed and `L` to set the length (1-256 steps). Speed and length are displayed in the editor title bar.
+
+The script loops over its length just like a pattern. Context words like `step`, `iter`, and `phase` work as expected, counting within the script's own cycle.
+
+## Keybindings
+
+| Key | Action |
+|-----|--------|
+| `F11` | Open periodic script view |
+| `Enter` | Focus editor |
+| `Esc` | Unfocus and save |
+| `Ctrl+E` | Evaluate |
+| `Ctrl+S` | Toggle stack display |
+| `S` | Set speed (unfocused) |
+| `L` | Set length (unfocused) |