Let the page fling work anywhere, with a setting to turn it off

A fling toward a free side of the active page now offers a page at any
zoom or pan position, not only once that edge is on screen. If the
side's plus is visible it pulses as before; otherwise an "Add page"
button appears at that edge of the screen, tapped through the same
palm-checked gesture as the plus.

Settings → Pen & touch gets "Swipe to add pages" (on by default).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GaoZtJQZwLXkEgWs8twCia

README.md

@@ -23,7 +23,7 @@ The image builds the PWA and serves it with nginx. Put an HTTPS reverse proxy in
 ## Using it
 
 - **Tools** (bottom bar): Text `T`, Pen `P`, Highlighter `H`, Eraser `E`, Import PDF, Undo/Redo, zoom. The pen's eraser end erases too.
-- **Pages**: the "+" circles beside the active page add a page there (a quick finger fling past a free edge highlights that side's "+"); `Alt+Arrow` moves to (or creates) the neighbour. Right-click a page or use its `⋯` button to insert, resize or delete it.
+- **Pages**: the "+" circles beside the active page add a page there (a quick finger flick toward a free side offers one there; turn it off under Settings → Pen & touch); `Alt+Arrow` moves to (or creates) the neighbour. Right-click a page or use its `⋯` button to insert, resize or delete it.
 - **Grid**: the faint background grid has one cell per active page; Settings → Appearance can hide it or subdivide it.
 - **Importing a PDF** into a non-empty canvas shows every free spot; click one to place the chain. Into a blank canvas it simply replaces the empty page. The Files panel can also import a PDF as a new canvas.
 - **View**: wheel/trackpad pans, `Ctrl`+wheel or pinch zooms, `Ctrl+0` fits the page, `Ctrl+9` shows the whole tree, space-drag or middle-drag pans.