feat(emacs): Add prebuilt Doom option using nix-doom-emacs-unstraightened

Implement pre-built Doom Emacs packages for the live USB image, eliminating
the need to run `doom sync` after first boot.

Changes:
- Add nix-doom-emacs-unstraightened flake input
- Add homeModule to all three module sets (nixos, unstable, darwin)
- Add `prebuiltDoom` option to emacs role (default: false)
- Enable prebuiltDoom for live-usb configuration
- Pin custom packages in packages.el for deterministic builds:
  - claude-code-ide, gptel-tool-library, beads

When prebuiltDoom=true, all Doom packages are compiled at nix build time
using emacs-overlay. The doom configuration is stored in the nix store
(read-only), and no `doom sync` is required at runtime.

This is ideal for:
- Live USB images
- Immutable/reproducible systems
- Offline deployments

Closes: nixos-configs-1wd

home/roles/emacs/doom/packages.el

@@ -51,11 +51,21 @@
 
 ;; (package! org-caldav)
 
+;; Note: Packages with custom recipes must be pinned for nix-doom-emacs-unstraightened
+;; to build deterministically. Update pins when upgrading packages.
+
 (package! gptel :recipe (:nonrecursive t))
 
 (package! claude-code-ide
-  :recipe (:host github :repo "manzaltu/claude-code-ide.el"))
+  :recipe (:host github :repo "manzaltu/claude-code-ide.el")
+  :pin "760240d7f03ff16f90ede9d4f4243cd94f3fed73")
 
 (package! gptel-tool-library
   :recipe (:host github :repo "aard-fi/gptel-tool-library"
-           :files ("*.el")))
+           :files ("*.el"))
+  :pin "baffc3b0d74a2b7cbda0d5cd6dd7726d6ccaca83")
+
+(package! beads
+  :recipe (:type git :repo "https://codeberg.org/ctietze/beads.el.git"
+           :files ("lisp/*.el"))
+  :pin "f40a6461d3c0fa0969311bbb6a1e30d1bba86c88")