feat: repo archive/unarchive + completion install

- fgj repo {archive,unarchive}: toggle a repo's archived state via
  EditRepo with *bool Archived. Archive prompts for confirmation
  (requires --yes in non-TTY envs); unarchive is reversible, no prompt.
  Accepts positional owner/name or -R flag; -R wins when both given.

- fgj completion install [shell]: idempotent install of completion
  scripts to shell-standard locations. Auto-detects shell from $SHELL
  if omitted. Paths: bash → XDG (or brew prefix on macOS), zsh →
  ~/.zsh/completions/_fgj, fish → ~/.config/fish/completions/fgj.fish.
  --system (bash only) prints the sudo command for /etc paths without
  writing. --dry-run prints the target path without writing.
  Compares existing-file contents before overwrite to stay idempotent.

Both files built by sub-agents in parallel. Build + vet + test clean.

cmd/repo_archive.go

@@ -0,0 +1,163 @@
+package cmd
+
+import (
+	"fmt"
+
+	"code.gitea.io/sdk/gitea"
+	"forgejo.zerova.net/public/fgj-sid/internal/api"
+	"forgejo.zerova.net/public/fgj-sid/internal/config"
+	"github.com/spf13/cobra"
+)
+
+var repoArchiveCmd = &cobra.Command{
+	Use:   "archive [owner/name]",
+	Short: "Archive a repository",
+	Long: `Mark a repository as archived. Archived repositories remain visible but
+become read-only: pushes, issues, pull requests, and releases are disabled.
+
+The target repo may be passed as a positional argument, via -R/--repo, or
+auto-detected from the current git context. If both positional and -R are
+given, the -R flag wins.`,
+	Example: `  # Archive a specific repo (prompted confirmation)
+  fgj repo archive owner/name
+
+  # Archive the current repo without prompting
+  fgj repo archive --yes
+
+  # Archive using the -R flag
+  fgj repo archive -R owner/name -y`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: runRepoArchive,
+}
+
+var repoUnarchiveCmd = &cobra.Command{
+	Use:   "unarchive [owner/name]",
+	Short: "Unarchive a repository",
+	Long: `Clear the archived flag on a repository, restoring normal read-write
+behaviour.
+
+The target repo may be passed as a positional argument, via -R/--repo, or
+auto-detected from the current git context. If both positional and -R are
+given, the -R flag wins.`,
+	Example: `  # Unarchive a specific repo
+  fgj repo unarchive owner/name
+
+  # Unarchive the current repo
+  fgj repo unarchive`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: runRepoUnarchive,
+}
+
+func init() {
+	repoCmd.AddCommand(repoArchiveCmd)
+	repoCmd.AddCommand(repoUnarchiveCmd)
+
+	addRepoFlags(repoArchiveCmd)
+	repoArchiveCmd.Flags().BoolP("yes", "y", false, "Skip the confirmation prompt")
+	addJSONFlags(repoArchiveCmd, "Output updated repository as JSON")
+
+	addRepoFlags(repoUnarchiveCmd)
+	repoUnarchiveCmd.Flags().BoolP("yes", "y", false, "Skip the confirmation prompt (unused; kept for symmetry with archive)")
+	addJSONFlags(repoUnarchiveCmd, "Output updated repository as JSON")
+}
+
+// resolveRepoTarget returns owner/name honouring the "optional positional OR
+// -R flag" pattern used elsewhere in the CLI: -R wins when both are supplied.
+func resolveRepoTarget(cmd *cobra.Command, args []string) (string, string, error) {
+	var repo string
+	if len(args) > 0 {
+		repo = args[0]
+	}
+	if r, _ := cmd.Flags().GetString("repo"); r != "" {
+		repo = r
+	}
+	return parseRepo(repo)
+}
+
+func runRepoArchive(cmd *cobra.Command, args []string) error {
+	owner, name, err := resolveRepoTarget(cmd, args)
+	if err != nil {
+		return err
+	}
+
+	slug := fmt.Sprintf("%s/%s", owner, name)
+	skipConfirm, _ := cmd.Flags().GetBool("yes")
+
+	if !skipConfirm {
+		if !ios.IsStdinTTY() {
+			return fmt.Errorf("refusing to archive %s without a TTY; pass -y/--yes to confirm non-interactively", slug)
+		}
+		prompt := fmt.Sprintf("Archive %s? This disables issues/PRs/pushes. [y/N]: ", slug)
+		answer, err := promptLine(prompt)
+		if err != nil {
+			return err
+		}
+		if answer != "y" && answer != "Y" && answer != "yes" && answer != "Yes" && answer != "YES" {
+			fmt.Fprintln(ios.ErrOut, "Aborted.")
+			return nil
+		}
+	}
+
+	cfg, err := config.Load()
+	if err != nil {
+		return err
+	}
+	client, err := api.NewClientFromConfig(cfg, "", getDetectedHost(), getCwd())
+	if err != nil {
+		return err
+	}
+
+	archived := true
+	opt := gitea.EditRepoOption{Archived: &archived}
+
+	ios.StartSpinner("Archiving repository...")
+	repository, _, err := client.EditRepo(owner, name, opt)
+	ios.StopSpinner()
+	if err != nil {
+		return fmt.Errorf("failed to archive %s: %w", slug, err)
+	}
+
+	if wantJSON(cmd) {
+		return outputJSON(cmd, repository)
+	}
+
+	cs := ios.ColorScheme()
+	fmt.Fprintf(ios.Out, "%s Archived %s\n", cs.SuccessIcon(), slug)
+	return nil
+}
+
+func runRepoUnarchive(cmd *cobra.Command, args []string) error {
+	owner, name, err := resolveRepoTarget(cmd, args)
+	if err != nil {
+		return err
+	}
+
+	slug := fmt.Sprintf("%s/%s", owner, name)
+
+	cfg, err := config.Load()
+	if err != nil {
+		return err
+	}
+	client, err := api.NewClientFromConfig(cfg, "", getDetectedHost(), getCwd())
+	if err != nil {
+		return err
+	}
+
+	archived := false
+	opt := gitea.EditRepoOption{Archived: &archived}
+
+	ios.StartSpinner("Unarchiving repository...")
+	repository, _, err := client.EditRepo(owner, name, opt)
+	ios.StopSpinner()
+	if err != nil {
+		return fmt.Errorf("failed to unarchive %s: %w", slug, err)
+	}
+
+	if wantJSON(cmd) {
+		return outputJSON(cmd, repository)
+	}
+
+	cs := ios.ColorScheme()
+	fmt.Fprintf(ios.Out, "%s Unarchived %s\n", cs.SuccessIcon(), slug)
+	return nil
+}