docs: redesign README onboarding

[egdev6]

Closes #3

Type

• Bug fix
• New feature
• Documentation only
• Code refactoring
• Maintenance/tooling
• Breaking change

Summary

• Redesign the README with a stronger visual hierarchy and progressive onboarding.
• Document the real conversational and direct plan/apply workflows with copy-paste examples.
• Clarify capabilities, safety boundaries, verification, releases, and repository structure.

Changes

File	Change
README.md	Add the visual hero, navigation, quick start, usage examples, safety model, verification guidance, release policy, and repository map.

Test plan

• npm test — 26 passed, 0 failed.
• git diff --check passed.
• All 27 local links and document anchors validated.
• Documented commands and paths checked against Pi package behavior and repository implementation.
• Shellcheck applicability reviewed; no shell scripts changed.

Contributor checklist

• Linked approved issue docs: improve README onboarding and usage #3.
• Added exactly one type:* label.
• Verified every documented executable command.
• Confirmed no skill implementation artifacts changed.
• Updated only documentation.
• Used a Conventional Commit message.
• Added no Co-Authored-By trailers.