docs: canonicalize README onboarding

[br4vesirrobin]

Summary

• identify kontor-cli and its move-only mailbox safety boundary precisely
• replace retired repository URLs with r3dlex/cli-kontor
• provide one dry-run-first Quick Start with observable configuration success
• distinguish rules-only classify output from the process LLM fallback
• limit rebuild/heal claims to the pipeline's fixed SCAN_FOLDERS scope
• gitignore sensitive rules/evolved/ decision logs and document safe retention
• preserve generated AI-SDLC markers

Current head validation

• uv run pytest tests/unit/readme_contract_test.py -v --tb=short (3 passed)
• uv run pytest tests/unit/ -v --tb=short (248 passed)
• uv run ruff check src/ tests/
• uv run ruff format --check src/ tests/
• uv run mypy src/ --ignore-missing-imports
• uv build
• bash scripts/validate-rules.sh
• bash scripts/archgate.sh structural .rules.ts
• python3 .ai/bin/validate-ai-sdlc.py
• uvx prek run --all-files
• git diff --check
• git check-ignore -v rules/evolved/example_rule_adjustments.json

Story: G008