docs: Correct unsupported agent-management command examples

[sam-saffron-jarvis]

What was wrong

The agents guide advertised direct export, directory import, and a top-level agents gist command that are not implemented. Its clear example supplied an unsupported second argument and implied a single-key reset. Exporting the untouched built-in reviewer is also rejected.

What changed

• Use agents export gist my-reviewer, using the filesystem copy already shown.
• Use agents import gist <gist-url-or-id> and remove the nonexistent top-level Gist example.
• Use agents clear reviewer and explicitly label it as clearing ALL preferences.
• Note the gh prerequisite and authentication requirements.

Only docs-site/content/guides/agents.md changed.

How it was verified

Inspected current command definitions and registrations in cmd/agents.go:

agentsExportCmd.AddCommand(agentsExportGistCmd)
agentsImportCmd.AddCommand(agentsImportGistCmd)

Their child signatures are gist <agent-name> and gist <gist-url-or-id>; the parents have no execution handlers. The clear command declares:

Use:   "clear <agent>",
Short: "Clear all preferences for an agent",
Args:  cobra.ExactArgs(1),

runAgentsPrefClear calls config.ClearAgentPreferences(agentName), whose implementation in internal/config/config.go removes the entire agent entry with delete(prefs, agentName). runAgentsExportGist rejects agent.Source == agents.SourceBuiltin with the message cannot export built-in agent ... Copy it first. The Gist command descriptions document the gh and authentication requirements.

Also ran the installed CLI's agents export --help, agents import --help, and agents clear --help: export/import each list only gist, and clear reports term-llm agents clear <agent> [flags] and “Clear all preferences for an agent.” No Gists were published and no preferences were cleared.

Validation passed:

• cd docs-site && hugo --quiet --destination /tmp/docs-build-228c7211
• git diff --stat and git diff --check
• git diff --name-only confirmed documentation only.

No internal links were changed.