feat: add Home Manager refactoring plan and initial structure

- Add comprehensive Home Manager refactoring plan document
- Create initial Home Manager directory structure with user configs
- Add modular Emacs configuration for Home Manager integration
- Update system configurations for Home Manager compatibility
- Preserve existing functionality while preparing for migration

🤖 Generated with [Claude Code](https://claude.ai/code)

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

home-manager/modules/emacs/default.nix

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+# Shared Emacs module for Home Manager
+# Contains common Emacs functionality that can be shared across users
+
+{ config, lib, pkgs, ... }:
+
+{
+  # Shared Emacs configuration that can be imported by users
+  # Contains package sets, profile definitions, and common configurations
+  
+  # This will contain the migrated packageSets from the current emacs.nix
+  # and shared Emacs functionality
+}

home-manager/modules/emacs/nix-integration.nix

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+# Emacs Nix integration module
+# Contains Nix tool integration and environment variable configuration
+
+{ config, lib, pkgs, ... }:
+
+{
+  # Nix tool integration for Emacs
+  # Environment variables for Nix-provided tools
+  # LSP server configurations
+  # Formatter integrations
+}

home-manager/modules/emacs/profiles.nix

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+# Emacs profile definitions for Home Manager
+# Contains the profile-based package selection logic
+
+{ config, lib, pkgs, ... }:
+
+{
+  # Profile-based Emacs package configurations
+  # This will contain the migrated packageSets logic from current emacs.nix
+  
+  # Profiles: essential, minimal, development, workstation
+  # Package selection based on profile type
+}