docs(zsh): require canonical option spellings

[ss-o]

Summary

• Add zsh/options/canonical-spelling to the routed organization Zsh scripting standard.
• Require underscore-separated canonical names such as local_options and no_auto_pushd in commands, emulate, conditionals, parameters, generated arguments, examples, and newly authored comments.
• Preserve option names that originate dynamically from captured runtime state or user input.
• Keep guidance in the existing canonical organization surface, without adding a repository-local duplicate or a narrow CI guard.

Part of #565.
Coordinates with z-shell/zi#449.

Instruction impact review

1. Classification: Required, task-scoped organization guidance for Zsh source, with machine-readable policy metadata and validation.
2. Consumers: Codex, Claude Code, Copilot, Gemini CLI, humans, and CI in every repository context performing Zsh work.
3. Canonical owner: .github/instructions/zsh-scripting.instructions.md, coordinated with lib/zsh-standard-policy.json, remains the correct owner.
4. Duplication or conflict: No equivalent or contradictory organization rule was found. No Zi-local instruction or second source of truth is added.
5. Routing: No manifest change is needed because the existing Zsh scripting surface and route already select the canonical standard.
6. Delivery: Required instruction routing delivers the rule to supported runtimes without depending on an optional hook, skill, or CI guard.
7. Generated output and limits: The public validators and suites pass. The private generated instruction composite is current and all private instruction tests pass.

Verification

• python3 scripts/validate-agent-policy.py: passed.
• python3 -m unittest scripts/test_validate_agent_policy.py -v: 84 tests passed.
• python3 scripts/validate-zsh-standard-policy.py: passed.
• python3 -m unittest scripts/test_validate_zsh_standard_policy.py -v: 99 tests passed.
• git diff --check: passed.
• Local commit hook: passed.
• Private workspace verification against the combined state also passed: generated instructions were current and all 89 private instruction tests passed.

Agent handoff

• Status: Ready for review
• Current state: Canonical guidance is complete on code/zsh-option-spelling-standard; the corresponding Zi normalization is prepared separately.
• Blockers: None in this PR. Project 28 status mutation was previously rate-limited.
• Next steps: Review this policy change, then review the linked Zi normalization PR.
• Related tracker/issues: initiative: restore truthful Zi lifecycle and update contracts #565 and refactor(core): consolidate duplicate helpers and naming drift zi#449