docs: feat: add deployments show subcommand (#134)

## Summary

This work relates to PR #125 

## Motivation

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Closes #<!-- issue number -->

## Changes

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-->

-

## Test strategy

<!-- How did you verify this works? Check all that apply. -->

- [ ] Added/updated unit tests
- [ ] Manual CLI testing (`poly <command>`)
- [ ] Tested against a live Agent Studio project
- [x] N/A (docs, config, or trivial change)

## Checklist

- [ ] `ruff check .` and `ruff format --check .` pass
- [ ] `pytest` passes
- [x] No breaking changes to the `poly` CLI interface (or migration path
documented)
- [ ] Commit messages follow [conventional
commits](https://www.conventionalcommits.org/)

## Screenshots / Logs

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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: AaronForinton

docs/docs/reference/cli.md

@@ -455,8 +455,14 @@ Examples:
 poly deployments list
 poly deployments list --env live
 poly deployments list --details
+poly deployments show abc123def
+poly deployments show abc123def --env live
 ~~~
 
+#### `poly deployments list`
+
+List deployments for the project.
+
 | Flag | Description |
 |---|---|
 | `--env` | Environment to list deployments for. Choices: `sandbox`, `pre-release`, `live`. Defaults to `sandbox`. |
@@ -547,6 +553,7 @@ poly init --region us-1 --account_id 123 --project_id my_project --json
 poly project create --region us-1 --account_id my-account --name my-project --json
 poly chat --json -m 'Hello'
 poly chat --json --input-file ./script.txt
+poly deployments show abc123def --json
 poly deployments list --json
 poly deployments promote --from <id> --to pre-release --force --json
 poly deployments rollback --to <id> --force --json
@@ -588,13 +595,21 @@ The exact fields vary by command. Common fields include:
 | `poly init --json` | `success`, `root_path` |
 | `poly project create --json` | `success`, `root_path` (via init); on error: `success`, `error` |
 | `poly chat --json` | `conversations` (array); optional `push` (when `--push` is used) |
+| `poly deployments show --json` | `success`, `deployment`, `active_deployment_hashes`, `included_deployments`, `is_rollback` |
 | `poly deployments promote --json` | `success`, `from_hash`, `to_env`, `message`, `included_deployments`; `dry_run` when `--dry-run` is used |
 | `poly deployments rollback --json` | `success`, `target_hash`, `message`, `reverted_deployments`; `dry_run` when `--dry-run` is used |
 
 For `poly branch delete --json`, when a branch that was the current branch is deleted, the response also includes `"switched_to": "main"`.
 
 For `poly branch merge --json`, a successful merge returns `{ "success": true }`. When conflicts or errors are present, the response includes `"conflicts"` and `"errors"` arrays containing the raw conflict and error objects from the platform.
 
+For `poly deployments show --json`, the response includes:
+
+- `deployment` — the full deployment record for the requested version hash.
+- `active_deployment_hashes` — a map of environment names to the currently active version hash in each environment.
+- `included_deployments` — the list of sandbox deployments included since the predecessor version in the queried environment.
+- `is_rollback` — `true` if the deployment is a rollback to an older version.
+
 Error responses always include `{ "success": false, "error": "...", "traceback": "..." }`.
 
 !!! info "`init` with `--json` requires explicit flags"