fix: resolve golangci-lint failures and .gitignore scope issue

- cmd/server/main.go: acknowledge w.Write return value (errcheck)
- internal/store/mongo.go: use errors.Is for ErrNoDocuments (errorlint)
- .golangci.yml: add linter config scoped to relevant linters
- .gitignore: scope /server to root only (was blocking cmd/server/ directory)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitignore

@@ -2,5 +2,5 @@
 cast-ghl-provider
 /tmp/
 
-# compiled binary (root)
-server
+# compiled binary (root-level only, not cmd/server/ directory)
+/server

.golangci.yml

@@ -0,0 +1,25 @@
+linters:
+  enable:
+    - errcheck
+    - govet
+    - staticcheck
+    - gosimple
+    - ineffassign
+    - unused
+    - errorlint
+    - gocritic
+    - revive
+
+linters-settings:
+  revive:
+    rules:
+      - name: exported
+        disabled: true
+
+issues:
+  exclude-rules:
+    # Test files can use dot-imports and assertion helpers freely
+    - path: _test\.go
+      linters:
+        - errcheck
+        - gocritic

cmd/server/main.go

@@ -85,5 +85,5 @@ func main() {
 func healthCheck(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusOK)
-	w.Write([]byte(`{"status":"ok","service":"cast-ghl-provider"}`))
+	_, _ = w.Write([]byte(`{"status":"ok","service":"cast-ghl-provider"}`))
 }

internal/store/mongo.go

@@ -2,6 +2,7 @@ package store
 
 import (
 	"context"
+	"errors"
 	"time"
 
 	"go.mongodb.org/mongo-driver/v2/bson"
@@ -61,7 +62,7 @@ func (s *Store) GetToken(ctx context.Context, locationID string) (*TokenRecord,
 	filter := bson.D{{Key: "location_id", Value: locationID}}
 	var record TokenRecord
 	err := s.collection.FindOne(ctx, filter).Decode(&record)
-	if err == mongo.ErrNoDocuments {
+	if errors.Is(err, mongo.ErrNoDocuments) {
 		return nil, nil
 	}
 	if err != nil {