feat(scrapper): add PostgreSQL storage and scheduled link updates

[666mxvbee]

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[666mxvbee]

Summary

This pull request completes the Scrapper persistence and scheduled update-processing stage for LinkTracker.

It adds PostgreSQL-backed storage, SQL migrations, raw SQL and EF Core repository implementations, scheduled GitHub/StackOverflow link checks, batched and parallel processing, and tests based on Testcontainers and WireMock.

Changes

• Added PostgreSQL persistence for chats, links, subscriptions, and tags.
• Added SQL migrations executed programmatically with DbUp.
• Added Docker Compose PostgreSQL setup and environment-based database configuration.
• Added raw SQL repositories using Npgsql.
• Added ORM repositories using EF Core.
• Added configurable repository selection through Database:AccessType.
• Added tag CRUD API and database-level tag filtering.
• Added scheduled link update processing.
• Added configurable batch size and parallelism.
• Added GitHub update detection for new issues and pull requests.
• Added StackOverflow update detection for new answers and comments.
• Added notification sender abstraction from Scrapper to Bot.
• Added HTTP notification sender implementation.
• Added README run instructions and project badges.

Testing

• dotnet restore
• dotnet build
• dotnet test

The test suite covers migrations, SQL and ORM repositories, tag CRUD, update preview formatting, GitHub and StackOverflow API handling, batch processing, parallel processing, and isolated failure handling.