feat(cli): add setup select for explicit multi-host plugin install

[knqiufan]

Note

The implementation described below was merged through #1314 because that PR was stacked on this branch. After
rebasing onto the latest master, this PR has no remaining file diff and does not require a separate merge.

Which issue or RFC does this PR close?

Closes #1301.

Rationale for this change

Installing PowerContext for several coding agents currently requires one fail-closed setup <host> command per
integration. Chaining those commands aborts on the first unavailable CLI, while PATH-driven auto-install would treat
CLI presence as user intent and could unexpectedly modify every detected host.

This PR adds an opt-in orchestration command that installs only the integrations selected by the user, preserves the
existing single-host commands, and isolates failures so one host does not prevent the remaining selections from being
processed.

What changes are included in this PR?

• Add powercontext setup select for the supported host catalog: codex, claude-code, dsh, openclaw,
  opencode, pi, and hermes.
• Reuse the existing installers without scanning PATH to build or filter the catalog.
• Support repeatable --host options for scripts and CI. Interactive TTY sessions without --host display the
  catalog and accept numbers or names; --json and non-TTY usage require --host.
• Preserve host-specific defaults. Claude Code and OpenClaw use http://127.0.0.1:8000, and OpenClaw uses
  --scope-mode agent. Explicit --server-url and --scope-mode values are forwarded to the applicable hosts.
• Run existing post-install diagnostics for Codex, DSH, OpenCode, Pi, and Hermes before reporting success.
• Report selected installer or verification failures per host and continue processing the other selections.
• Report unselected hosts as skipped and print the Hermes memory setup guidance after a successful Hermes install.
• Keep empty powercontext setup help-only and keep every setup <host> command fail-closed.
• Update the English and Chinese installation, troubleshooting, and CLI reference documentation.
• Add focused coverage for selection, failure isolation, TTY and non-TTY behavior, JSON output, option forwarding,
  host-specific defaults, post-install verification, and unchanged single-host behavior.

Are there any user-facing changes?

Yes. The following optional command is new:

powercontext setup select --host codex --host dsh
powercontext setup select --host openclaw --scope-mode agent
powercontext setup select --host codex --json

There is no breaking API or storage-format change. Existing per-host setup commands retain their current behavior,
and setup does not start the PowerContext Server or launch a host process.

How was this change tested?

• uv lock --check
• uv run ruff check src/powercontext/cli/hosts.py src/powercontext/cli/system.py tests/test_setup_select.py
• uv run ruff format --check src/powercontext/cli/hosts.py src/powercontext/cli/system.py tests/test_setup_select.py
• uv run pytest tests/test_setup_select.py tests/test_system_cli.py tests/test_dsh_cli.py tests/test_hermes_cli.py tests/test_openclaw_cli.py tests/test_pi_cli.py
• uv run ty check
• uv run zensical build -s in a clean worktree

AI usage statement

AI assistance was used for implementation and review against the issue contract. The command surface, failure
isolation rules, and acceptance criteria follow #1301.

[Teingi]

LGTM