refactor(install): restore fresh-install flow, drop transform.sh and personas

Long-standing gaps in post-install.sh plus cleanup:

- post-install.sh:18 was `sudo pacman -S paru` on the wrong
  assumption paru had landed in [extra]. Verified: paru/paru-bin
  are AUR-only. Restored the original git-clone + makepkg
  bootstrap, added the rust buildep that archinstall does not
  pull in.
- post-install.sh never installed AUR extras — walker, elephant,
  waypaper, stasis, themes all silently skipped. Now pulls
  packages/aur.txt after moonarch-git.
- packages/official.txt: drop glab, go, npm (unused) and rustup
  (only needed for the paru build, handled imperatively now).
- packages/aur.txt: add walker-bin (was missing entirely).
- transform.sh + legacy update.sh shim removed — transform was
  never used in practice.
- Apollo persona block out of CLAUDE.md, prior DECISIONS entries
  rewritten from Apollo/Ragnar to ClaudeCode.
- README Transform section and scripts/ listing trimmed.
- lib.sh ABOUTME updated — only post-install.sh sources it now.

packages/aur.txt

@@ -11,6 +11,7 @@ colloid-catppuccin-theme-git
 otf-openmoji
 
 # Niri / Wayland Extras
+walker-bin
 elephant-desktopapplications-bin
 elephant-clipboard-bin
 elephant-bluetooth-bin