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>

hosts/terra/configuration.nix

@@ -18,7 +18,6 @@ in
     ../../services/desktop/desktop-hyprland.nix
     ../../services/desktop/desktop-apps.nix
     ../../services/desktop/librechat.nix
-    ../../services/desktop/hermes-agent.nix
   ];
 
   networking.hostName = "terra";
@@ -98,10 +97,9 @@ in
     loadModels = [ "gemma4:12b" "qwen3.6:35b-a3b" ];
     # Ollama truncates context far below the model's real window unless
     # told otherwise (the OpenAI-compat /v1 route it's reached through has
-    # no way to set this per-request — see services/desktop/hermes-agent.nix,
-    # which points at this server and mirrors the same number in
-    # model.context_length). 131072 chosen as the practical ceiling after
-    # load-testing with real prompts, not just idle `ollama ps` checks:
+    # no way to set this per-request). 131072 chosen as the practical
+    # ceiling after load-testing with real prompts, not just idle
+    # `ollama ps` checks:
     # 32768 (31.6k-token prompt) and 65536 (40.8k-token prompt) both stayed
     # 100% GPU with VRAM barely moving (~10.1G / ~10.67G of 16G) — KV cache
     # cost barely grows with context, likely sliding-window/local attention