chore: handle lightweight vs full plugin in shell file generation

[scappuccino-grid]

Distinguish between lightweight (rosetta@rosetta) and full (core@rosetta, grid@rosetta) plugins when deciding whether to generate shell files in Phase 2 of init-workspace-flow. Full plugins ship all instructions bundled so shells are not needed; lightweight plugins require shells to enable skills, agents, and workflows. When plugin type cannot be detected, ask the user with an explanation and suggest lightweight (the recommended install) as the default.

Also fixes inconsistent sentinel phrase used for plugin mode detection ("Rosetta plugin is already active" → "RUNNING AS A PLUGIN").

[github-actions]

Rosetta Triage Review

Summary: This PR improves the init-workspace-flow by distinguishing between lightweight (rosetta@rosetta) and full (core@rosetta, grid@rosetta) plugin types when deciding whether to generate shell files in Phase 2. It also fixes an inconsistent sentinel phrase used for plugin mode detection.

Findings:

• All 4 changed files are instruction/workflow documents under instructions/r2/core/ — no runtime code affected
• The sentinel phrase fix ("Rosetta plugin is already active" → "RUNNING AS A PLUGIN") is a consistency bug fix; existing deployments relying on the old phrase would have silently misbehaved
• The plugin_type = unknown branch correctly gates on HITL before writing any files — safe fallback behavior
• The HITL question text is clear, well-structured, and nudges users toward the recommended lightweight install
• Output contract of Phase 1 is properly updated (plugin_type added to state and validation checklist)
• Phase 2 workflow context input list is updated to include state.plugin_type — consistent across all documents

Suggestions:

• Consider adding a note in the pitfalls section of init-workspace-flow-shells.md clarifying that plugin_type = unknown should never persist past Phase 2 (it must be resolved before proceeding)
• The branch name chore/shell_f_handling has a typo (shell_f likely intended as shell_file) — cosmetic only, no action needed

Automated triage by Rosetta agent

[isolomatov-gd]

There is a misunderstanding. Lightweight plugin should not be using instructions/r2/core/rules/plugin-files-mode.md, as such it should not even BE detected as plugin. Moreover lightweight is just a way to simplify two manual actions: installing MCP and adding bootstrap file.

[isolomatov-gd]

@scappuccino-grid Why do we need further?