Update docs to match backend key rename and CWD behavior

- cli-config.yaml.example: env_type → backend everywhere, matching the
  documented config key that hermes_cli/config.py and README already use
- cli-config.yaml.example: added comments clarifying cwd is a path
  INSIDE the target environment for non-local backends
- AGENTS.md: updated terminal.cwd description to explain "." only
  resolves to host CWD for the local backend
- .env.example: updated TERMINAL_CWD comment to warn against using
  host-local paths with remote backends, lists per-backend defaults

.env.example

@@ -48,8 +48,10 @@ TERMINAL_MODAL_IMAGE=nikolaik/python-nodejs:python3.11-nodejs20
 
 
 # Working directory for terminal commands
-# For CLI: "." means current directory (resolved automatically from config.yaml)
-# For containers (docker/singularity/modal): absolute path inside the container
+# For local backend: "." means current directory (resolved automatically)
+# For remote backends (ssh/docker/modal/singularity): use an absolute path
+#   INSIDE the target environment, or leave unset for the backend's default
+#   (/root for modal, / for docker, ~ for ssh). Do NOT use a host-local path.
 # Usually managed by config.yaml (terminal.cwd) — uncomment to override
 # TERMINAL_CWD=.