docs: Update README to reflect gen.isdb=false as default

[Copilot]

gen.isdb defaults to false in application.yml, but documentation still described true (database mode) as the default.

Proposed Changes

1. Update root README.md — flip default description to gen.isdb=false, swap startup command sections so no-database mode is presented as default
2. Update src/main/resources/file/README.md — same changes as root README
3. Update application.yml comment — 默认无数据库(false)为内存存储，true为数据库版本

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request

Reviewing Maintainer

• Label as either enhancement, bug, documentation, style or dependencies
• Verify design and implementation

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Feature Request] README更新</issue_title>
<issue_description>### Checklist

• I searched exising issues and no one else requests similar feature.
• I think that 25%+ users are positive towards this feature.

Describe the feature

现在gen.isdb=false 是默认值，请更新README

Additional context

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature Request] README更新 #236

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[naming-conventions-bot]

Thank you for following naming conventions! 😻

[mergify]

Thanks for opening this pull request!
Please check out the Contributing Guidelines.

[mergify]

@Copilot
Wrong PR Title: [WIP] Update README to reflect default value of gen.isdb
Please check Contributing Guidelines for more information.

[what-the-diff]

PR Summary

• Clarification of Configuration Instructions in application.yml
  • An update in the comment was made to better describe how to configure the database option. The new instruction shows that setting the option to false means using memory for storage, while setting it to true enables the use of a database.

[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