Initial commit: Chatter — assistive-writing app for reMarkable Paper Pro Move

Direct-framebuffer ink pipeline (stock-quality strokes), finger-wipe erase,
growable scrolling canvas with color-ghost cleanup, bidirectional toggle with a
persistent 4-finger return launcher, instant button feedback. Includes prebuilt
aarch64 binaries (dist/), build/deploy/install scripts, a user guide, and a
complete technical reference.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

doc/Chatter_user_guide.md

@@ -0,0 +1,58 @@
+# Chatter — How to Use It
+
+Chatter is a simple writing screen. You write with the pen; the person you are
+talking with reads what you wrote. That's it.
+
+## Writing
+
+- **Write with the pen**, just like on paper.
+- The pen's color and thickness are whatever is set in the normal reMarkable
+  screen. (To change them, see "Changing the pen" below.)
+
+## The two buttons (top of the screen)
+
+```
+ ┌──────┐                              ┌───────┐
+ │ Back │                              │ Clear │
+ └──────┘                              └───────┘
+```
+
+- **Clear** (top right) — erases everything and gives you a fresh page.
+- **Back** (top left) — leaves Chatter and goes to the normal reMarkable screen.
+
+A button turns **gray** the moment you touch it, so you know it heard you. You
+can press a button with **either the pen or your finger**.
+
+## Erasing
+
+- **Erase a little:** rub a **finger** back and forth over what you want to
+  remove, like erasing pencil with your fingertip.
+- **Erase everything:** tap **Clear**.
+- You can also flip the pen over and use the **eraser end**, like a pencil.
+
+## More room to write
+
+- **Two fingers, drag up or down** to scroll, when you want more space than one
+  screen. The page follows your fingers.
+- (After scrolling, the screen may blink once to clean itself up. That's normal.)
+
+## Going back and forth
+
+- **Leave Chatter:** tap **Back**.
+- **Return to Chatter** from the normal reMarkable screen: place **four fingers
+  on the screen and hold** for about a second.
+
+## Changing the pen (color / thickness)
+
+Chatter copies the pen you last used in the normal reMarkable screen. To change
+it:
+
+1. Tap **Back** to go to the normal screen.
+2. Open a page, pick the pen, color, and thickness you want, and **write a little
+   with it**.
+3. **Go back to the document list** (this is what saves your choice).
+4. Return to Chatter (four-finger hold). Your new pen is now used.
+
+---
+
+*Questions or problems during setup go to Matt.*