feat(02-03): add prompt template files

- prompts/__init__.py: Package marker
- context_recovery.md: Session context recovery prompt
- command_mapping.md: User input to GSD command mapping
- error_recovery.md: User-friendly error message generation

All templates use {{variable}} syntax for substitution.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gsd-openclaw/src/gsd_openclaw/prompts/__init__.py

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+# Prompt templates for GSD-OpenClaw

gsd-openclaw/src/gsd_openclaw/prompts/command_mapping.md

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+# Command Mapping
+
+Map the following user input to a GSD slash command.
+
+## User Input
+{{user_input}}
+
+## Available Commands
+- /gsd:new-project <name> - Create a new project
+- /gsd:use <project> - Switch to a project
+- /gsd:status - Show current status
+- /gsd:plan - Run planning phase
+- /gsd:ship - Ship current phase
+- /gsd:help - Show help
+
+## Current Context
+- Project: {{current_project}}
+- Phase: {{current_phase}}
+
+## Instructions
+Determine the most appropriate command based on the user input and context.

gsd-openclaw/src/gsd_openclaw/prompts/context_recovery.md

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+# Context Recovery
+
+You are resuming a GSD session that was interrupted.
+
+## Session Information
+- **Project**: {{project_name}}
+- **Last Active**: {{last_active_at}}
+- **Current Phase**: {{current_phase}}
+- **Commands Executed**: {{command_count}}
+
+## Last Known State
+{{last_output_snapshot}}
+
+## Instructions
+Continue from where the session left off. Do not repeat completed steps.

gsd-openclaw/src/gsd_openclaw/prompts/error_recovery.md

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+# Error Recovery
+
+An error occurred while processing a GSD command.
+
+## Error Details
+**Command**: {{command}}
+**Error**: {{error_message}}
+
+## Context
+- Project: {{project_name}}
+- Phase: {{current_phase}}
+
+## Instructions
+Generate a user-friendly error message in Chinese that:
+1. Explains what went wrong
+2. Suggests possible solutions
+3. Offers next steps the user can take