refactor: move hive-c0re options to hyperhive namespace (#612)

- Move options.services.hive-c0re → options.hyperhive.c0re
- Add options.hyperhive.enable to auto-enable c0re + subsystems
- Add deprecation alias for services.hive-c0re.enable (backward compat)
- Update doc references in README, flake.nix, docs, harness-base.nix
- Simplifies config: 'hyperhive.enable = true' now enables everything

Existing operator configs using services.hive-c0re.enable will
continue to work but emit a deprecation warning. Aligns the option
namespace with the existing hyperhive.* family (matrix, forge, domain).

fixes #612

flake.nix

@@ -225,7 +225,7 @@
         agent-base = ./nix/templates/agent-base.nix;
         manager = ./nix/templates/manager.nix;
         # The hive-c0re module wants `pkgs.hyperhive` for its default
-        # `services.hive-c0re.package`. To avoid making operators apply an
+        # `hyperhive.c0re.package`. To avoid making operators apply an
         # overlay (which would also pollute their host pkgs with our
         # build), we thread the package straight from this flake's
         # `packages.<system>.default` via a `hyperhivePackage` argument.
@@ -237,7 +237,7 @@
           hyperhiveAssets = system: self.packages.${system}.assets;
           hyperhiveFlake = "${self}";
           # Per-container toplevels — wired into `system.extraDependencies`
-          # when `services.hive-c0re.preBuildAgentTemplates` is on so the
+          # when `hyperhive.c0re.preBuildAgentTemplates` is on so the
           # host system closure pre-fetches the heavy build inputs (#97).
           # Defined only for x86_64-linux because nixosConfigurations are
           # hardcoded to that system; the option's default keeps the
@@ -252,7 +252,7 @@
         # in hive-forge). Intended usage:
         #
         #   imports = [ hyperhive.nixosModules.default ];
-        #   services.hive-c0re.enable = true;
+        #   hyperhive.enable = true;
         #
         default = self.nixosModules.hive-c0re;
       };