Add workflow orchestrator enhancements

[cryptosebek]

Summary

This PR makes the workflow orchestrator usable directly from an installed Pi package while keeping project-level customization available.

Runtime changes

• Resolve workflows and bundled tool extensions from the package when a project override is not present.
• Materialize missing workflow and agent defaults into the project on first use without overwriting existing files.
• Discover bundled agents when no project agent directory exists, while preserving user/project precedence.
• Add shorthand command support: /workflow "goal", optional workflow names, quoted arguments, and --model <id>.
• Persist the selected run model and fall back to the active Pi model when resuming older state. Agent frontmatter models remain higher priority.
• Resolve configured extension paths against the project or package installation.
• Improve subagent model-error messages with actionable /model and agent-frontmatter hints.
• Surface startup and resume configuration errors as workflow notifications instead of unhandled rejections.

Documentation and configuration

• Update bundled PM, developer, and verifier model defaults to openrouter/free.
• Update the project guide and README for package defaults, shorthand commands, and model overrides.
• Refresh development dependency versions.

Tests

• Add coverage for package fallback, default materialization, extension resolution, command tokenization, model selection, and model-error formatting.
• Retain and extend workflow clarification regression coverage.
• Remove duplicate extension-resolution and model-selection tests.

Validation

• 207 tests passing
• TypeScript typecheck passing
• ESLint passing
• Prettier checks passing
• git diff --check passing

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Honor the workflow model override before agent defaults

When a user starts /workflow --model <id> "goal", startWorkflow stores that model in currentState.model, but this call passes agent.model to pickModel first. Because the bundled PM/developer/verifier agent files all define model: openrouter/free, the requested run model is never used for those subagents (the PM runner uses the same precedence below), so the new CLI flag silently has no effect unless users edit or remove every agent model line.

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