docs: align user guide with conversation flow

[unagi]

目的\nユーザー視点のREADMEに再構成し、LLM向けの制約はSKILL/ガイドへ整理する。\n\n## 変更点\n- ユーザー向けREADMEを会話フロー中心に全面改稿\n- SKILL.mdの参照先をユーザー向けREADMEに明確化\n- 入力ガイド/例の更新（氏名の区切り、学歴/職歴の入退学・入退社）\n- 免許・資格欄の行数調整\n- CLI出力にバックアップ案内を追加\n- 職務経歴書ベストプラクティスに具体ルール・記載例を追記\n\n## テスト\n- uv run poe check-all\n\n## 破壊的変更\n- なし

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.96%. Comparing base (720bb29) to head (987cac9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #27   +/-   ##
=======================================
  Coverage   90.96%   90.96%           
=======================================
  Files          22       22           
  Lines        1936     1936           
=======================================
  Hits         1761     1761           
  Misses        175      175           

Flag	Coverage Δ
unittests	90.96% <ø> (ø)

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud