terra: finish removing Hermes Agent (module import + secrets)

Follow-up to e5ba1bf — that commit only staged the deleted module file.
Drops the flake module import, opencode_go_api_key/telegram_bot_token
secrets, and the stale hermes-agent.nix cross-reference in ollama's
context_length comment.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

flake.nix

@@ -33,7 +33,7 @@
     };
     authentik-nix.url = "github:nix-community/authentik-nix";
     nix-flatpak.url = "github:gmodena/nix-flatpak";
-    # Hermes Agent (see services/desktop/hermes-agent.nix) — Tier 2 platform
+    # Hermes Agent (see hosts/jupiter/hermes-agent.nix) — Tier 2 platform
     # per its own docs (best-effort Nix support, can break on any upstream
     # commit), so pinned like everything else via flake.lock rather than
     # followed loosely.
@@ -111,7 +111,6 @@
             sops-nix.nixosModules.sops
             home-manager.nixosModules.home-manager
             inputs.nix-flatpak.nixosModules.nix-flatpak
-            inputs.hermes-agent.nixosModules.default
             ./hosts/terra/configuration.nix
           ];
         };