fix: add extra_files to copy source directories into Docker build context

GoReleaser creates a temporary build context with only binaries, but our
Dockerfiles are multi-stage builds that need the full source code to
compile. Added extra_files to copy necessary directories.

Files copied per image:
- gohoarder-server: go.mod, go.sum, cmd, pkg, internal, config
- gohoarder-scanner: go.mod, go.sum, cmd, pkg, internal, config
- gohoarder-migrate: go.mod, go.sum, cmd, pkg, internal, migrations
- gohoarder-frontend: frontend/ directory (Node.js source)
- gohoarder-gateway: no extra files needed (static config)

This fixes the build context error:
"Seems like you tried to copy a file that is not available in the
build context."

.goreleaser.yaml

@@ -146,6 +146,13 @@ dockers_v2:
       - "--label=org.opencontainers.image.version={{ .Version }}"
       - "--label=org.opencontainers.image.created={{ .Date }}"
       - "--label=org.opencontainers.image.revision={{ .FullCommit }}"
+    extra_files:
+      - go.mod
+      - go.sum
+      - cmd
+      - pkg
+      - internal
+      - config.yaml.example
 
   # 2. Website - Frontend Dashboard
   - id: gohoarder-frontend
@@ -167,6 +174,8 @@ dockers_v2:
       - "--label=org.opencontainers.image.version={{ .Version }}"
       - "--label=org.opencontainers.image.created={{ .Date }}"
       - "--label=org.opencontainers.image.revision={{ .FullCommit }}"
+    extra_files:
+      - frontend
 
   # 3. Scanning Engine - Background scanner worker
   - id: gohoarder-scanner
@@ -192,6 +201,13 @@ dockers_v2:
       - "--label=org.opencontainers.image.version={{ .Version }}"
       - "--label=org.opencontainers.image.created={{ .Date }}"
       - "--label=org.opencontainers.image.revision={{ .FullCommit }}"
+    extra_files:
+      - go.mod
+      - go.sum
+      - cmd
+      - pkg
+      - internal
+      - config.yaml.example
 
   # 4. Gateway - Nginx reverse proxy for unified deployment
   - id: gohoarder-gateway
@@ -238,6 +254,13 @@ dockers_v2:
       - "--label=org.opencontainers.image.version={{ .Version }}"
       - "--label=org.opencontainers.image.created={{ .Date }}"
       - "--label=org.opencontainers.image.revision={{ .FullCommit }}"
+    extra_files:
+      - go.mod
+      - go.sum
+      - cmd
+      - pkg
+      - internal
+      - migrations
 
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