feat: setup script, evaluation walkthrough, portals, and batch retry

[RajjjAryan]

Summary

Addresses 4 open issues in one PR:

1. Setup script — replaces #25 (Docker)

• setup.sh — one command installs Node deps, Playwright Chromium, copies config templates, runs doctor
• Docker was overkill; a bash script is simpler and more appropriate for a CLI tool
• README updated with bash setup.sh option

2. Evaluation walkthrough — closes #7

• docs/evaluation-walkthrough.md — full A-F scoring example with realistic data
• Shows each block's output, scoring logic, and final verdict
• Helps new users understand what career-copilot produces

3. 10 more company portals — closes #2

Added to templates/portals.example.yml:
Stripe, Datadog, Cloudflare, Figma, Notion, Databricks, Scale AI, Supabase, Dagger, Modal

4. Rate limiting & retry logic — closes #26

Updated modes/batch.md with:

• 2s delay between worker batches
• 10s backoff on 429 (rate limit) responses
• 3s spacing for same-domain requests
• Max 3 attempts per URL (1 initial + 2 retries)
• Non-retryable errors: login walls, 404s, removed listings

Testing

All 58 tests pass, 0 failures.