feat: integrate m3ta-home for centralized user profiles

- Add m3ta-home as flake input (ssh://gitea@code.m3ta.dev/m3tam3re/m3ta-home)
- Rewrite hosts/common/users/m3tam3re.nix to use m3ta-home.lib.mkHome
- Central host profile mapping (context + sets per hostname)
- Per-host feature flags for desktop vs server hosts
- Extract Hyprland monitor layouts to hosts/<name>/home.nix
- Per-host home.nix auto-imported if file exists

BREAKING: This replaces the old home/m3tam3re/<host>.nix system.
The old home/ directory is kept but no longer referenced.
It should be removed in a follow-up commit after verification.

flake.nix

@@ -43,6 +43,11 @@
     rose-pine-hyprcursor.url = "github:ndom91/rose-pine-hyprcursor";
     nix-colors.url = "github:misterio77/nix-colors";
 
+    m3ta-home = {
+      url = "git+ssh://gitea@code.m3ta.dev/m3tam3re/m3ta-home.git";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     agents = {
       # url = "path:/home/m3tam3re/p/AI/AGENTS";
       url = "git+https://code.m3ta.dev/m3tam3re/AGENTS";