feat(repos): add repo edit subcommand (#928)

## Summary
- Add `tea repo edit` subcommand to update repository properties via the Gitea API
- Support flags: `--name`, `--description`/`--desc`, `--website`, `--private`, `--template`, `--archived`, `--default-branch`
- Boolean-like flags use string type to distinguish "not set" from "false", following the pattern in `releases/edit.go`

## Test plan
- [x] `go build ./...` passes
- [x] `go vet ./...` passes
- [x] `tea repo edit --help` shows all flags correctly
- [x] Manual test: `tea repo edit --private true` on a test repo
- [x] Manual test: `tea repo edit --name new-name --description "new desc"` on a test repo

Reviewed-on: https://gitea.com/gitea/tea/pulls/928
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-committed-by: Bo-Yi Wu <appleboy.tw@gmail.com>

cmd/repos.go

@@ -32,6 +32,7 @@ var CmdRepos = cli.Command{
 		&repos.CmdRepoFork,
 		&repos.CmdRepoMigrate,
 		&repos.CmdRepoRm,
+		&repos.CmdRepoEdit,
 	},
 	Flags: repos.CmdReposListFlags,
 }