cli: add doctor for examples, environment, secret configuration, and test vectors

[dgenio]

Add a lightweight doctor/preflight command for local agent-kernel setup. It should check required environment variables such as WEAVER_KERNEL_SECRET, example fixtures, token signing/verification test vectors, policy config, and docs quickstart consistency. Output should support human text and JSON. Fail non-zero on invalid setup; warn on insecure demo-only configuration.

[dgenio]

Closing as completed — this is implemented and merged.

The weaver-kernel doctor preflight command shipped in v0.11.0 via PR #148 (commit e593456, on main at e78a863).

Evidence in the current codebase:

• src/weaver_kernel/cli/_doctor.py — checks Python version, WEAVER_KERNEL_SECRET (warns on insecure demo-only config), optional extras (policy/mcp/otel), and self-test vectors for token signing/verification (_check_token_vector) and the audit chain (_check_audit_chain_vector). Exits non-zero only when a check errors (broken setup).
• --json and human-text output both supported (cmd_doctor, build_doctor_parser).
• Wired as a subcommand of the weaver-kernel console script ([project.scripts] in pyproject.toml), documented in docs/cli.md.
• CHANGELOG [0.11.0] records it: "weaver-kernel doctor preflight-checks the environment, optional extras, and token / audit-chain self-test vectors (cli: add doctor for examples, environment, secret configuration, and test vectors #124)."

If any sub-check you intended (e.g. example-fixture or quickstart-consistency validation) is still missing, please open a focused follow-up.

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