[EVI-12]: shorten evidence README

[riddim-developer-bot]

Summary

• Cuts the root README from 375 lines / 1,765 words to 161 lines / 565 words.
• Keeps the README focused on purpose, quick start, minimal app usage, command overview, one CI example, safety guidance, and links.
• Leaves detailed command and launch material in docs/ and Examples/ instead of duplicating it in the root README.

Review basis

Sampled GitHub's README guidance plus public README patterns from React, VS Code, freeCodeCamp, and Oh My Zsh. The applied pattern is: short front door, quick path to first use, links to deeper docs.

Verification

• wc -l README.md && wc -w README.md -> 161 lines, 565 words.
• swift run evidence -- --help passed and README command references match the exposed CLI surface.
• git diff --check origin/main..HEAD passed.
• README stale/internal scan returned no matches for removed commands, internal runner labels, local paths, or private Riddim repo references.
• swift test --filter WorkflowSafetyTests passed: 3 tests, 0 failures.

Follow-up to EVI-12 / PR #42.