fix: Add default seed.json to match config

[chenmingyong0423]

When cloning the repository and building the project using:

go build ./cmd/registry
./registry

the application fails to start because the default seed file path (data/seed.json) does not exist in the repo:

Failed to read seed file: failed to read file: open data/seed.json: The system cannot find the file specified.

To address this, this PR adds a data/seed.json file to ensure the app can run successfully with default settings.

Changes:

• Added data/seed.json as a default seed file to align with the default configuration
• Contents are copied from the latest available seed file (e.g. seed_2025_05_16.json)
• Ensures the application runs out-of-the-box without requiring additional environment configuration
• Developers can still override the seed file path using the SEED_FILE_PATH environment variable

Let me know if you'd prefer to solve this differently (e.g., by changing the default path or improving fallback behavior).

[chenmingyong0423]

Hi! Just wondering — would it perhaps be more straightforward to update the envDefault tag in the Config.SeedFilePath field to point directly to data/seed_2025_05_16.json instead?

Adding a seed.json file works, but it might not be the most future-proof solution, especially if the seed file name keeps changing over time. Curious to hear your thoughts — happy to adjust the PR if needed!