docs: reposition README as developer-first security platform

[sonukapoor]

Rewrites the README to reframe CVE Lite CLI beyond a scanner — positioning it as a developer-native approach to dependency security that shifts detection from CI pipelines to the terminal before code is pushed.

Changes:

• Opens with the problem (reactive CI tooling, alert fatigue, no actionable remediation) before introducing the product
• "A different model" section frames the tool's approach as a deliberate design choice
• Features rewritten as developer outcomes rather than capability lists
• Workflow integration consolidated into a single section covering local dev, CI, GitHub Actions, and enterprise/offline
• "Real-world validation" frames the case studies as documented evidence of impact, not demos
• Philosophy section articulates the developer-native security argument
• Forward-looking "What's next" section introduces the broader vision without claiming unbuilt features
• Closes with a standalone quotable line

Closes #240