Address PR review comments from Ben, Shiridi, and Benjamin

- Delete unused duplicate diagram (complete-guide-fig-8)
- Frameworks: simplify intro text (remove SSR patterns)
- Overview: simplify step 3, IMPORTANT→NOTE, fix secret wording
- Overview: align LICENSE_KEY note with Ben's suggestion
- Getting Started: apply Shiridi's panel UI wording fixes
- Getting Started: fix dotenv override issue (Benjamin's report)
- Getting Started: align TIP folder name example with mkdir step

Author: kemister85