feat(issues): add dependency management commands

Add commands to manage issue dependencies using the Gitea API:
- `tea issues dependencies <index>` - list dependencies
- `tea issues dependencies add <index> <dep>` - add a dependency
- `tea issues dependencies remove <index> <dep>` - remove a dependency

Supports cross-repo dependencies with owner/repo#index syntax.
Supports all output formats (table, json, csv, etc.).

Closes #4

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/issues.go

@@ -63,6 +63,7 @@ var CmdIssues = cli.Command{
 		&issues.CmdIssuesEdit,
 		&issues.CmdIssuesReopen,
 		&issues.CmdIssuesClose,
+		&issues.CmdIssuesDependencies,
 	},
 	Flags: append([]cli.Flag{
 		&cli.BoolFlag{