fix: add missing backend deps/env and stabilize frontend CI

[Emart29]

Motivation

• Ensure backend features (Supabase, SQL parsing, encryption) can run by adding required dependencies and runtime placeholders.
• Prevent CI frontend failures caused by Next.js environment validation and lockfile/installer mismatches.
• Fix small frontend artifacts (JSON, escaped quotes) that blocked lint/build validation.

Description

• Updated backend/pyproject.toml to add supabase, sqlglot, and cryptography to runtime dependencies to enable providers, SQL parsing, and encryption support.
• Expanded backend/.env.example with ENCRYPTION_KEY, FRONTEND_URL, SUPABASE_SERVICE_KEY, ENVIRONMENT, and GROQ_API_KEY placeholders to document required runtime settings.
• Modified frontend/package.json to add the reactflow dependency and normalize JSON formatting.
• Fixed quoting in frontend/src/app/(dashboard)/page.tsx to remove escaped-quote issues.
• Updated .github/workflows/ci.yml to set default frontend environment variables (NEXT_PUBLIC_API_URL, NEXT_PUBLIC_SUPABASE_URL, NEXT_PUBLIC_SUPABASE_ANON_KEY) so next.config.js validation passes in CI, and replaced pnpm steps with npm/package-lock.json-based installs to align with the repo lockfile.

Testing

• Ran Python syntax check: cd backend && find . -name "*.py" -exec python -m py_compile {} \; which completed successfully. (success)
• Validated frontend JSON: cd frontend && cat package.json | python -m json.tool which completed successfully. (success)
• Scanned frontend source for escaped-quote issues with rg which reported no problems. (success)
• Attempted cd frontend && npm install which failed in this environment with a registry 403 Forbidden error preventing a local install. (failure due to external registry)
• Attempted NEXT_PUBLIC_API_URL=http://localhost:8000 NEXT_PUBLIC_SUPABASE_URL=https://example.supabase.co NEXT_PUBLIC_SUPABASE_ANON_KEY=test-key npm run build which failed because node_modules were not available from the failed install and the build reported module-not-found errors. (failure)
• CI change: added default envs in the workflow so next.config.js will not throw for missing NEXT_PUBLIC_* vars during CI runs (prevents the prior cause of CI frontend failures).

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Codex Task