#15746: docs(nodes): add exec cwd validation errors to troubleshooting

Add two new error codes to the troubleshooting guide: - `Exec cwd does not exist: <path>` — cwd doesn't exist on the node - `Exec cwd is not a directory: <path>` — cwd is a file, not a dir These errors were introduced in #15454 (node-host cwd validation). Previously, an invalid cwd would silently fall back to $HOME, which could cause confusing behavior. The new errors give clear guidance on what went wrong and how to fix it. Includes zh-CN translation. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> Updates the node troubleshooting docs to document two new `nodes.run` exec working-directory validation errors (`cwd` missing on node, or `cwd` points to a file). The English doc change is straightforward and fits the existing "Common node error codes" section. However, the PR also manually edits `docs/zh-CN/nodes/troubleshooting.md`, which is treated as generated content in this repo; that should be produced via the docs i18n pipeline (English source → glossary/TM tweaks if needed → `scripts/docs-i18n`) to avoid drift/being overwritten. <h3>Confidence Score: 4/5</h3> - Mostly safe to merge, but fix the docs i18n workflow issue first. - The English doc update is low-risk and consistent. The only blocking issue found is that the PR directly edits `docs/zh-CN/**`, which the repo treats as generated output; that will drift or be overwritten unless the change is made through the translation pipeline. - docs/zh-CN/nodes/troubleshooting.md _{Last reviewed commit: 67d1da5} <!-- greptile_other_comments_section --> _{(5/5) You can turn off certain types of comments like style [here](https://app.greptile.com/review/github)!} **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->