feat: comprehensive boilerplate improvements

Security & Stability:
- Add Next.js 16 proxy.ts for BetterAuth cookie-based auth protection
- Add rate limiting for API routes (src/lib/rate-limit.ts)
- Add Zod validation for chat API request bodies
- Add session auth check to chat and diagnostics endpoints
- Add security headers in next.config.ts (CSP, X-Frame-Options, etc.)
- Add file upload validation and sanitization in storage.ts

Core UX Components:
- Add error boundaries (error.tsx, not-found.tsx, chat/error.tsx)
- Add loading states (skeleton.tsx, spinner.tsx, loading.tsx files)
- Add toast notifications with Sonner
- Add form components (input.tsx, textarea.tsx, label.tsx)
- Add database indexes for performance (schema.ts)
- Enhance chat UX: timestamps, copy-to-clipboard, thinking indicator,
  error display, localStorage message persistence

Polish & Accessibility:
- Add Open Graph and Twitter card metadata
- Add JSON-LD structured data for SEO
- Add sitemap.ts, robots.ts, manifest.ts
- Add skip-to-content link and ARIA labels in site-header
- Enable profile page quick action buttons with dialogs
- Update Next.js 15 references to Next.js 16

Developer Experience:
- Add GitHub Actions CI workflow (lint, typecheck, build)
- Add Prettier configuration (.prettierrc, .prettierignore)
- Add .nvmrc pinning Node 20
- Add ESLint rules: import/order, react-hooks/exhaustive-deps
- Add stricter TypeScript settings (exactOptionalPropertyTypes,
  noImplicitOverride)
- Add interactive setup script (scripts/setup.ts)
- Add session utility functions (src/lib/session.ts)

All changes mirrored to create-agentic-app/template/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,43 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: '[BUG] '
+labels: bug
+assignees: ''
+---
+
+## Describe the bug
+
+A clear and concise description of what the bug is.
+
+## To Reproduce
+
+Steps to reproduce the behavior:
+
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+## Expected behavior
+
+A clear and concise description of what you expected to happen.
+
+## Screenshots
+
+If applicable, add screenshots to help explain your problem.
+
+## Environment
+
+- OS: [e.g. Windows, macOS, Linux]
+- Node.js version: [e.g. 20.10.0]
+- Browser: [e.g. Chrome, Safari]
+- Package manager: [e.g. pnpm, npm]
+
+## Additional context
+
+Add any other context about the problem here.
+
+## Possible Solution
+
+If you have suggestions on a fix for the bug, please describe it here.