feat(pstack): sync upstream 0.15.15 guidance

[HustleCoding]

Why

Upstream added prompting references and refreshed its guidance after our last sync. This ports the five new pstack commits through version 0.15.15 into the Codex fork.

What changed

• Add copyable prompting recipes and a Codex usage guide for investigation, verification, design, and longer runs.
• Offer setup once when relevant configuration is missing, while answering the user's question.
• Make unlimited budget target Max reasoning, with supported-effort fallback. Balanced preserves existing role efforts.

Scope

The port record records every reviewed commit. Keep Codex-only Sol/Luna/Astra routes, existing help discovery, and three-seat panels. Exclude upstream's provider switch, Cursor cloud integration, and Bot UI. Installation preserves the existing global model configuration.

Verification

• Upstream checker reports up-to-date; the repository audit passes for all 50 skills.
• All 25 existing tests pass. Both modified skills pass skill validation, and local documentation links resolve.
• These checks validate packaging and existing tooling; they do not establish future LLM workflow behavior.

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[devin-ai-integration]

Devin Review found 1 potential issue.