feat: show coder sharing in CLI help and reference docs (#30141)

`coder sharing` has been hidden since it was added behind an experiment,
although Shared Workspaces is GA and the prose docs already use it.

This removes `Hidden: true`, regenerates `docs/reference/cli/sharing/*`,
and adds the pages to the docs manifest.
The shared workspaces guide and the persistent shared workspaces
tutorial now link to the new reference.

**Behavior change:** `coder sharing` and its subcommands now appear in
`coder --help`.
The commands themselves are unchanged.
The `sharing remove --user/--group` help text previously said "to share
the workspace with"; it now says "to remove from the workspace".

<details>
<summary>Decisions</summary>

- Follow-up not in this PR: `DELETE /workspaces/{workspace}/acl` has no
CLI caller.

</details>

Closes [CLI-22](https://linear.app/codercom/issue/CLI-22)

_This PR was generated by Coder Agents on behalf of @nickvigilante._

docs/tutorials/persistent-shared-workspaces.md

@@ -159,6 +159,8 @@ Verify current sharing status at any time:
 coder sharing status oncall-sre/oncall-workspace
 ```
 
+For every subcommand and flag, see the [`coder sharing` reference](../reference/cli/sharing/index.md).
+
 ## 6. Automate access changes (optional)
 
 For use cases with frequent rotation (such as on-call shifts), you can integrate