Add Dependabot configuration for automated dependency updates (#15)

* Initial plan

* Add comprehensive dependabot.yml configuration

Co-authored-by: PhantomDave <34485699+PhantomDave@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: PhantomDave <34485699+PhantomDave@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -0,0 +1,102 @@
+# Dependabot configuration for automated dependency updates
+# See https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+
+version: 2
+updates:
+  # .NET NuGet packages for backend API
+  - package-ecosystem: "nuget"
+    directory: "/PhantomDave.BankTracking.Api"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "09:00"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "dotnet"
+      - "backend"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+
+  # .NET NuGet packages for data layer
+  - package-ecosystem: "nuget"
+    directory: "/PhantomDave.BankTracking.Data"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "09:00"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "dotnet"
+      - "backend"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+
+  # .NET NuGet packages for library/domain layer
+  - package-ecosystem: "nuget"
+    directory: "/PhantomDave.BankTracking.Library"
+    schedule:
+      interval: "weekly"
+      day: "monday"
+      time: "09:00"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "dotnet"
+      - "backend"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+
+  # npm packages for Angular frontend
+  - package-ecosystem: "npm"
+    directory: "/frontend"
+    schedule:
+      interval: "weekly"
+      day: "tuesday"
+      time: "09:00"
+    open-pull-requests-limit: 5
+    labels:
+      - "dependencies"
+      - "npm"
+      - "frontend"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+    ignore:
+      # Ignore Angular major version updates to avoid breaking changes
+      - dependency-name: "@angular/*"
+        update-types: ["version-update:semver-major"]
+
+  # Docker base images
+  - package-ecosystem: "docker"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "wednesday"
+      time: "09:00"
+    open-pull-requests-limit: 3
+    labels:
+      - "dependencies"
+      - "docker"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"
+
+  # GitHub Actions workflows
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "thursday"
+      time: "09:00"
+    open-pull-requests-limit: 3
+    labels:
+      - "dependencies"
+      - "github-actions"
+    commit-message:
+      prefix: "chore(deps)"
+      include: "scope"