refactor(cli): remove redundant per-agent instruction files from webjs create templates

[vivek7405]

Problem

When scaffolding a new WebJs app (webjs create), the CLI currently emits multiple individual per-agent instruction files (CLAUDE.md, GEMINI.md, .cursorrules, .github/copilot-instructions.md, .cursor/hooks.json, .gemini/settings.json, .opencode/plugins/nudge-uncommitted.ts, etc.) to bridge rules to specific AI tools.

Now that .agents/skills/webjs/ (along with root AGENTS.md) is universally recognized as the open cross-agent standard by modern AI agents and harnesses (Cursor, Windsurf, Antigravity, opencode, Copilot, Claude Code), end-user WebJs apps no longer need individual per-agent instruction files or per-tool bridge configs. Emitting them creates unnecessary file clutter in freshly scaffolded end-user projects and risks instruction drift across agent-specific files.

Design / approach

1. Consolidate to Open Standard: End-user WebJs apps emitted by webjs create will ship only AGENTS.md, CONVENTIONS.md, and .agents/skills/webjs/ (plus .agents/rules/workflow.md), serving as the single cross-agent source of truth.
2. Remove Redundant Templates: Remove per-agent instruction and bridge files (CLAUDE.md, GEMINI.md, .cursorrules, .github/copilot-instructions.md) and per-agent tool hook directories (.cursor/, .gemini/, .opencode/) from packages/cli/templates/.
3. Streamline Generator Logic: Update packages/cli/lib/create.js (templateFiles array, PROSE_REWRITE Set, and file copy logic) to omit per-agent instruction files.
4. Update Generator Tests & Docs: Update packages/cli/test/create.test.js assertions, packages/cli/README.md, and documentation to reflect the streamlined cross-agent scaffold structure.

Implementation notes (for the implementing agent)

• Where to edit:
  • packages/cli/lib/create.js: Update templateFiles list (lines 570–625) and PROSE_REWRITE Set (lines 631–635).
  • packages/cli/templates/: Delete per-agent files (CLAUDE.md, GEMINI.md, .cursorrules, .github/copilot-instructions.md, .cursor/, .gemini/, .opencode/).
  • packages/cli/test/create.test.js: Update scaffold file tree assertions.
  • packages/cli/README.md & AGENTS.md: Update docs describing generated app layout.
• Invariants to respect:
  • .agents/skills/webjs/ and root AGENTS.md remain the authoritative cross-agent source of truth for WebJs applications.
  • Freshly scaffolded apps must pass webjs check and webjs doctor cleanly.
• Test + doc surfaces:
  • node --test packages/cli/test/create.test.js
  • E2E scaffold verification: npx webjs create test-app && ( cd test-app && npx webjs check )

Acceptance criteria

• Individual per-agent instruction files (CLAUDE.md, GEMINI.md, .cursorrules, .github/copilot-instructions.md) and per-agent tool directories (.cursor/, .gemini/, .opencode/) are removed from scaffold templates.
• webjs create emits only AGENTS.md, CONVENTIONS.md, and .agents/skills/webjs/ as the single cross-agent instruction surface.
• packages/cli/test/create.test.js passes with updated file tree assertions.
• A freshly scaffolded app boots and passes webjs check without errors.
• packages/cli/README.md and documentation reflect the streamlined scaffold layout.