feat(cli): add doctor integrations for first-class host status

[knqiufan]

Which issue or RFC does this PR close?

Closes #1313

Depends on #1311. Related to #1301; that issue stays with setup select.

Rationale for this change

setup select can install more than one first-class host, but diagnosis is still one fail-closed doctor <host> command per integration. Concatenating those commands exits 1 on the first missing CLI, so a machine that only has Codex looks unhealthy.

This PR adds a read-only overview that reports every first-class host, treats a missing CLI as missing instead of a command failure, and still fails when a present host is broken.

What changes are included in this PR?

• Add powercontext doctor integrations / --json over the shared feat(cli): add setup select for explicit multi-host plugin install #1311 catalog: codex, claude-code, dsh, pi, hermes.
• Reuse the existing diagnose functions through a lazy dispatcher. Do not flatten them into _diagnostics_ok. Do not scan PATH to build the menu. Do not install, start the Server, or launch a host.
• Classify each host from its CLI check plus its integration check (plugin, or package for Pi). Missing CLI + skipped integration → missing and does not fail the command. A present host with a failed CLI call or failed integration → exit 1.
• Empty doctor still checks only package + Server. doctor <host> remains fail-closed when that CLI is missing. setup select is unchanged.
• Docs: English and Chinese install, troubleshoot, and interfaces pages.
• Tests: tests/test_doctor_integrations.py covers the five-host JSON matrix, missing-CLI success, present plugin failure, present list-call failure, all-missing success, empty doctor not scanning hosts, and doctor codex still exiting 1 when Codex is missing.

This branch is stacked on #1311 (feat/cli-setup-select). Until that PR merges, the diff against master also includes setup select. The doctor-only change is commit b87faa8.

Are there any user-facing changes?

Yes. New optional command:

powercontext doctor integrations
powercontext doctor integrations --json

No breaking API or storage-format change. Empty doctor and doctor <host> keep their current behavior.

How was this change tested?

• python -m pytest tests/test_doctor_integrations.py
• python -m pytest tests/test_setup_select.py tests/test_system_cli.py tests/test_dsh_cli.py tests/test_hermes_cli.py tests/test_pi_cli.py
• ruff check on the changed Python files
• ty check on the changed Python files

AI usage statement

Used for implementation and review against the issue contract. The command surface, exit-code rules, and acceptance criteria follow #1313.