Improve repository discoverability

[Change3333]

What changed

• redesign the README first screen with a bilingual value proposition, badges, workflow, roadmap, FAQ, and Star call-to-action
• add a custom repository hero image without official platform trademarks
• add a real rendered product-interface preview that shows input, extraction output, and copy feedback
• use the consistent product name “抖音图文文案提取器” in both the page title and interface
• replace the unverifiable “百分百” claim with an accurate feature description
• add contributor, changelog, and security documentation
• add structured Bug and Feature issue forms
• add GitHub Actions CI for Python 3.10 and 3.12
• add unit tests for description filtering helpers

Why

The repository had no visual identity, product screenshot, contribution path, or automated checks. These changes improve search relevance, visitor trust, onboarding, and the likelihood that a useful visit converts into a Star or contribution.

User impact

Visitors can understand the project and its actual interface faster, install it with fewer steps, report issues consistently, and see automated validation status.

Validation

• GitHub Actions passed on Python 3.10 and 3.12
• 3 unit tests passed on both supported Python versions
• Python AST parsed successfully
• embedded JavaScript syntax passed
• all 4 GitHub YAML files parsed successfully
• product screenshot visually inspected at 900 × 850
• sensitive-pattern scan passed