docs(cmd,sync): Add async variant references

why: Help users discover async equivalents from sync API docs
what:
- cmd/index.md: Add "Async Variants" section listing AsyncGit, AsyncHg, AsyncSvn
- sync/index.md: Add "Async Variants" section listing AsyncGitSync, AsyncHgSync, AsyncSvnSync

Author: tony

docs/cmd/index.md

@@ -21,6 +21,16 @@ The `libvcs.cmd` module provides Python wrappers for VCS command-line tools:
 - {mod}`libvcs.cmd.hg` - Mercurial commands
 - {mod}`libvcs.cmd.svn` - Subversion commands
 
+### Async Variants
+
+Async equivalents are available in `libvcs.cmd._async`:
+
+- {class}`~libvcs.cmd._async.git.AsyncGit` - Async git commands
+- {class}`~libvcs.cmd._async.hg.AsyncHg` - Async mercurial commands
+- {class}`~libvcs.cmd._async.svn.AsyncSvn` - Async subversion commands
+
+See {doc}`/topics/asyncio` for usage patterns.
+
 ### When to use `cmd` vs `sync`
 
 | Module | Use Case |

docs/sync/index.md

@@ -14,6 +14,16 @@ versions.
 
 :::
 
+## Async Variants
+
+Async equivalents are available in `libvcs.sync._async`:
+
+- {class}`~libvcs.sync._async.git.AsyncGitSync` - Async git repository management
+- {class}`~libvcs.sync._async.hg.AsyncHgSync` - Async mercurial repository management
+- {class}`~libvcs.sync._async.svn.AsyncSvnSync` - Async subversion repository management
+
+See {doc}`/topics/asyncio` for usage patterns.
+
 ```{toctree}
 :caption: API