fix: clear the terminal before the install intro animation

The intro absolute-positions the logo grid and progress bar to fixed
screen rows, which assumes a clean screen. With prior shell output the
frames interleave with old text. Clear the screen at animation start in
both install.sh and install.ps1; the non-animated path is unchanged.

Author: elkaix

.changeset/install-clear-screen.md

@@ -0,0 +1,5 @@
+---
+'@pythoughts/pythinker-code': patch
+---
+
+Clear the terminal before the install script's animated intro so earlier shell output no longer interleaves with the logo animation.

apps/pythinker-web/public/install.ps1

@@ -148,6 +148,10 @@ function Stop-AntennaSpin {
 }
 
 function Write-LogoAnimated {
+  # The intro absolute-positions to screen rows (grid at 5-9, progress at
+  # 17), which assumes a clean screen. Clear it first — otherwise earlier
+  # shell output interleaves with the animation.
+  Write-Host -NoNewline "${ESC}[2J${ESC}[H"
   $rows = 5; $cols = 13
   $frameMs = 60; $staggerMs = 40
   if ($env:PYTHINKER_LOGO_FRAME_DELAY)   { try { $frameMs   = [int]([double]$env:PYTHINKER_LOGO_FRAME_DELAY   * 1000) } catch {} }

apps/pythinker-web/public/install.sh

@@ -327,6 +327,11 @@ print_logo_animated() {
   local FRAME_DELAY="${PYTHINKER_LOGO_FRAME_DELAY:-0.06}"
   local STAGGER_DELAY="${PYTHINKER_LOGO_STAGGER_DELAY:-0.04}"
 
+  # The whole intro absolute-positions to screen rows (grid at 5-9,
+  # progress at 17), which assumes a clean screen. Clear it first —
+  # otherwise earlier shell output interleaves with the animation.
+  printf '\033[2J\033[H'
+
   # Hide the text cursor while we redraw in place — otherwise the block
   # cursor on terminals like Terminal.app renders as a stray white block
   # at the cursor's current cell. Show it again before returning so the