Fix agent-specific paths in constitution update checklist

[maru0914]

Thank you for creating this amazing spec-driven development toolkit and open-sourcing it! 🙏

Problem

When running spec-kit init with Copilot, Gemini, or Cursor, the generated memory/constitution_update_checklist.md contains Claude-specific file paths, which can be confusing for users of other AI agents.

Before (Copilot selection)

- [ ] `/.claude/commands/plan.md` - Update if planning process changes
- [ ] `/.claude/commands/tasks.md` - Update if task generation affected  
- [ ] `/CLAUDE.md` - Update runtime development guidelines

After (Copilot selection)

- [ ] `/.github/prompts/plan.prompt.md` - Update if planning process changes
- [ ] `/.github/prompts/tasks.prompt.md` - Update if task generation affected
- [ ] `/.github/copilot-instructions.md` - Update runtime development guidelines

Solution

Replace hard-coded Claude paths with agent-specific placeholders that get resolved during template generation.

Changes

• memory/constitution_update_checklist.md: Replace Claude paths with readable placeholders (__COMMANDS_PLAN_PATH__, etc.)
• .github/workflows/scripts/create-release-packages.sh: Add placeholder replacement logic for each agent

Agent-specific paths

Agent	Plan Command	Tasks Command	Config File
Claude	/.claude/commands/plan.md	/.claude/commands/tasks.md	/CLAUDE.md
Copilot	/.github/prompts/plan.prompt.md	/.github/prompts/tasks.prompt.md	/.github/copilot-instructions.md
Gemini	/.gemini/commands/plan.toml	/.gemini/commands/tasks.toml	/GEMINI.md
Cursor	/.cursor/commands/plan.md	/.cursor/commands/tasks.md	/CURSOR.md

I think this change ensures users get relevant file paths in their constitution checklist, improving the developer experience across all supported AI agents