docs(bash): document the bashEnv hard dependency and dedupe the demo manifest

- tool-bash README (both languages) now shows the real four-service inject
  and attributes the session-persistence contributor to dsh-bash-env.
- pwsh-local README names the also-exported ENV_OVERRIDES/ENCODING_PREAMBLE.
- agent-spine-demo drops the duplicate bash-env devDependency key.

packages/examples/agent-spine-demo/package.json

@@ -79,7 +79,6 @@
     "@deepseek-ai/dsh-system-prompt": "workspace:^",
     "@deepseek-ai/dsh-tasks": "workspace:^",
     "@deepseek-ai/dsh-tasks-local": "workspace:^",
-    "@deepseek-ai/dsh-bash-env": "workspace:^",
     "@deepseek-ai/dsh-tool-bash": "workspace:^",
     "@deepseek-ai/dsh-tool-fs": "workspace:^",
     "@deepseek-ai/dsh-tool-goal": "workspace:^",