Rebind char cycling to ,/. instead of [/]

[ and ] needed a reach/shift on most layouts and felt awkward next to
the otherwise all-unshifted control scheme (hjkl, space, digits). ,
and . are adjacent, unshifted, easy to hit without looking away from
the canvas -- a natural prev/next pair. Old bindings kept as a fallback
rather than removed.

Verified both in isolation (Update() with a KeyMsg) and live over a
real SSH session -- the status-line ink swatch visibly cycles from █
to ▓ on a fresh connection. An initial live test after the rebind
appeared to fail, but that traced to a stale session left over from
the server restart, not an actual bug -- confirmed working correctly
on a fresh connection.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

game/view.go

@@ -42,7 +42,7 @@ func (m Model) renderIntro() string {
 		dim.Render("a shared doodle wall, one keystroke at a time") + "\n\n" +
 		"Everyone connected right now is drawing on the same canvas.\n" +
 		"Move with arrow keys or hjkl, space/enter to paint, backspace to\n" +
-		"erase. [ and ] cycle the ink character, 1-8 pick a color, c clears\n" +
+		"erase. , and . cycle the ink character, 1-8 pick a color, c clears\n" +
 		"everything for everyone (yes, really — it's a shared wall).\n\n" +
 		dim.Render("press any key to start")
 	return m.boxStyle().Render(body)
@@ -112,7 +112,7 @@ func (m Model) renderCanvas() string {
 
 	inkSwatch := m.style().Foreground(lipgloss.Color(inkPalette[m.inkColorIdx])).Render(string(charPalette[m.charIdx]))
 	dim := m.style().Foreground(lipgloss.Color("#777777"))
-	status := fmt.Sprintf("ink %s  (1-8 color, [ ] char)   peers: %d   %s",
+	status := fmt.Sprintf("ink %s  (1-8 color, , . char)   peers: %d   %s",
 		inkSwatch, m.canvas.PeerCount(), dim.Render("space paint · c clear · q quit"))
 
 	return m.boxStyle().Render(b.String() + "\n" + status)