docs: 프로젝트와 검증 중심으로 README 재구성

[tpals0409]

What this changes

Reframes the README in Korean around the project, Task workflow, architecture, design decisions, and dated verification evidence. Removes installation and execution instructions, leaves screenshot placeholders, and distinguishes current shared-checkout behavior from historical isolation claims. Updates CONTRIBUTING's removed README anchor and language convention.

Why

The portfolio README should explain the product and engineering decisions. The local, Claude Code, and Codex execution paths retain their actual permission distinctions, and historical benchmark results are explicitly scoped to the dated v1 audit.

How it was verified

• janus_server/.venv/bin/python -m pytest janus_server/tests/test_docs_match_code.py -q: 17 passed in 1.53s.
• README relative paths: all 17 resolve.
• git diff --check: exit 0.
• CI Python/Electron/renderer/bundle passed (1m25s); macOS packaging/MLX runtime passed (1m21s).
• Application/runtime code unchanged. The existing dependency-audit failure is documented below.

Checklist

• Focused documentation/code consistency tests passed
• No test was weakened
• Existing current checkout and provider boundaries preserved
• No packaging, MLX runtime, or application behavior changed

CI limitation

Production dependency audit failed on the unchanged Node dependency graph: 17 findings (11 high, 4 moderate, 2 low). No manifest or lockfile is changed by this PR. The dependency audit remains enabled and unchanged. See https://github.com/tpals0409/Janus/actions/runs/34437562897/job/102745709879.