feat: add actions management commands (#796)

## Summary

This PR adds comprehensive Actions secrets and variables management functionality to the tea CLI, enabling users to manage their repository's CI/CD configuration directly from the command line.

## Features Added

### Actions Secrets Management
- **List secrets**: `tea actions secrets list` - Display all repository action secrets
- **Create secrets**: `tea actions secrets create <name>` - Create new secrets with interactive prompts
- **Delete secrets**: `tea actions secrets delete <name>` - Remove existing secrets

### Actions Variables Management
- **List variables**: `tea actions variables list` - Display all repository action variables
- **Set variables**: `tea actions variables set <name> <value>` - Create or update variables
- **Delete variables**: `tea actions variables delete <name>` - Remove existing variables

## Implementation Details

- **Interactive prompts**: Secure input handling for sensitive secret values
- **Input validation**: Proper validation for secret/variable names and values
- **Table formatting**: Consistent output formatting with existing tea commands
- **Error handling**: Comprehensive error handling and user feedback
- **Test coverage**: Full test suite for all functionality

## Usage Examples

```bash
# Secrets management
tea actions secrets list
tea actions secrets create API_KEY    # Will prompt securely for value
tea actions secrets delete OLD_SECRET

# Variables management
tea actions variables list
tea actions variables set API_URL https://api.example.com
tea actions variables delete UNUSED_VAR
```

## Related Issue

Resolves #797

## Testing

- All new functionality includes comprehensive unit tests
- Integration with existing tea CLI patterns and conventions
- Validated against Gitea Actions API

Reviewed-on: https://gitea.com/gitea/tea/pulls/796
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Ross Golder <ross@golder.org>
Co-committed-by: Ross Golder <ross@golder.org>

docs/CLI.md

@@ -1269,6 +1269,110 @@ Unprotect branches
 
 **--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
 
+## actions, action
+
+Manage repository actions
+
+**--login**="": gitea login instance to use
+
+**--output, -o**="": output format [table, csv, simple, tsv, yaml, json]
+
+**--repo**="": repository to operate on
+
+### secrets, secret
+
+Manage repository action secrets
+
+#### list, ls
+
+List action secrets
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
+#### create, add, set
+
+Create an action secret
+
+**--file**="": read secret value from file
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
+**--stdin**: read secret value from stdin
+
+#### delete, remove, rm
+
+Delete an action secret
+
+**--confirm, -y**: confirm deletion without prompting
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
+### variables, variable, vars, var
+
+Manage repository action variables
+
+#### list, ls
+
+List action variables
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--name**="": show specific variable by name
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
+#### set, create, update
+
+Set an action variable
+
+**--file**="": read variable value from file
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
+**--stdin**: read variable value from stdin
+
+#### delete, remove, rm
+
+Delete an action variable
+
+**--confirm, -y**: confirm deletion without prompting
+
+**--login, -l**="": Use a different Gitea Login. Optional
+
+**--output, -o**="": Output format. (simple, table, csv, tsv, yaml, json)
+
+**--remote, -R**="": Discover Gitea login from remote. Optional
+
+**--repo, -r**="": Override local repository path or gitea repository slug to interact with. Optional
+
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