docs: add example prompts from claude-code-system-prompts
Added reference prompts for agent and tool implementations:
agents/explore/ - Codebase exploration agent prompt
agents/plan/ - Plan mode with system reminders
agents/task/ - Task execution agent prompt
agents/ - Main system prompt reference
tools/file/ - Read, Edit, Write, Glob tool descriptions
tools/shell/ - Bash with git commit/PR instructions
tools/search/ - Grep, WebSearch, WebFetch descriptions
Source: gitea:library/claude-code-system-prompts
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>