Add Dependabot configuration for automated dependency updates

[Copilot]

Adds .github/dependabot.yml to automate dependency updates across all package ecosystems in the monorepo.

Configuration

• NuGet (Monday): Three separate configs for Api, Data, and Library projects to track .NET dependencies independently
• npm (Tuesday): Frontend dependencies with major Angular version updates ignored to prevent breaking changes
• Docker (Wednesday): Base image updates for mcr.microsoft.com/dotnet/* and postgres:18-alpine
• GitHub Actions (Thursday): Workflow action version updates

Each ecosystem uses:

• 3-5 open PR limit to prevent noise
• chore(deps) conventional commit prefix
• Appropriate labels for filtering (dependencies, dotnet/npm/docker/github-actions, backend/frontend)

Updates are staggered across weekdays to distribute review load and CI resource usage.

Original prompt

Create a dependabot.yml file for auto-updates

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[Copilot]

Pull Request Overview

This PR adds a comprehensive Dependabot configuration to automate dependency updates across all package ecosystems in the monorepo.

• Configures weekly automated updates for NuGet, npm, Docker, and GitHub Actions dependencies
• Implements safeguards to prevent disruptive Angular major version updates
• Staggers update schedules across weekdays to distribute CI load and review effort