fix(colmena): expose colmenaHive for the nix-community evaluator (#361)

* fix(colmena): expose colmenaHive for the new evaluator

nixpkgs now ships the nix-community Colmena rewrite, whose default
evaluator reads an evaluated colmenaHive flake output instead of the raw
colmena hive. Without it every colmena apply recipe failed with
"does not provide attribute colmenaHive".

Add a colmena input pinned to the same v0.5.0 as nixpkgs and expose
colmenaHive = colmena.lib.makeHive <raw hive>, with the raw hive kept as
an internal binding rather than a flake output of its own.

* chore: clean up stale colmena and aquamarine references

- point the Colmena links at nix-community/colmena after the move
- rename the security-aquamarine-metrics test to youko-metrics (it
  already tested youko) and update the outputs README
- drop the commented aquamarine remote-builder example

lib/README.md

@@ -12,7 +12,7 @@ reduce code duplication and make it easier to add new machines.
    [nix-darwin](https://github.com/LnL7/nix-darwin)
 3. **`nixosSystem.nix`** - NixOS configuration generator
 4. **`colmenaSystem.nix`** - Remote deployment configuration for
-   [colmena](https://github.com/zhaofengli/colmena)
+   [colmena](https://github.com/nix-community/colmena)
 
 ### Specialized Module Generators