Configure Dependabot to group dependency updates

[Copilot]

Dependabot was not configured, resulting in no automated dependency updates. Added configuration to group updates by ecosystem, reducing PR noise.

Changes

• Go modules: All Go dependency updates grouped into single weekly PR
• GitHub Actions: All action version updates grouped into single weekly PR
• Labels: Auto-applied dependencies + ecosystem-specific labels for filtering

Configuration

Created .github/dependabot.yml:

version: 2
updates:
  - package-ecosystem: "gomod"
    directory: "/"
    schedule:
      interval: "weekly"
    groups:
      go-dependencies:
        patterns:
          - "*"

Both ecosystems use patterns: ["*"] to group all updates together rather than creating individual PRs per dependency.

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