Feature: Bootstrap script for new installs

bootstrap.sh installs everything listed in system/packages.txt (pacman,
AUR via yay, flatpak, official install scripts), auto-detects CPU
microcode and GPU drivers, enables services, links dotfiles with stow
and runs system/install.sh. Optional --svt-av1 installs
svt-av1-essential-git and rebuilds ffmpeg against it via
system/rebuild-ffmpeg.sh.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -39,7 +39,15 @@ mkdir Projects
 git clone ssh://git@gitea.thomasleewilliams.co.uk:2222/thomas/dotfiles.git
 ```
 
-Once that is complete, run this command:
+On a fresh install, run the bootstrap script. It installs drivers (auto-detected),
+every package in `system/packages.txt`, yay, flatpaks, then links the dotfiles and
+system config below:
+```console
+~/Projects/dotfiles/bootstrap.sh            # asks about the optional SVT-AV1 + ffmpeg rebuild
+~/Projects/dotfiles/bootstrap.sh --svt-av1  # or --no-svt-av1 to skip the question
+```
+
+To only link the dotfiles, run this command:
 ```console
 stow -d ~/Projects/dotfiles/ -t ~/ dotfiles
 ```